Fairly easy to install after reading instructions - we have several now in use and they’re solid!ORDER AND DELIVERYI received and installed the M210 Mechanical Keyless Entry Deadbolt yesterday (3 working days from order day). It was fulfilled by AAA Industrial Supply, and shipped via USPS. I ordered it late on Friday, it was fulfilled on Sunday, and Shipped on Monday since USPS doesn't work Sundays. Amazon's ETA was 10 days from shipping, but once I tracked it on the official USPS site it said 3 days, I was happy since my current deadbolt wasn't working. When the shipping box arrived it was in perfect condition as if it hadn't even been through transportation, and the internal retail box was perfect as well.INSTALLATIONThis Keyless Deadbolt was super easy to install, since I already had the deadbolt hole, it only required drilling one and a half (I'll explain the half) 5/16 holes from a template supplied that I matched to my deadbolt hole and taped to door. The first hole is drilled above deadbolt hole, and half at bottom edge of deadbolt hole, I had to use my drill to carve straight down since it's not that easy to drill half a hole on the edge of an existing hole. My door hinges are on the left so I had to unscrew and swap a pin to change the direction the lock pulls from, this took less than a minute. I put the hex screw extensions into lock and put them through newly drilled holes. I screwed the stability pin to back piece, and put locking pin through deadbolt and screwed the back on. I didn't change the combo yet because I wanted to see how long it'd take me to change the combo, and if it was worth changing frequently. The whole installation process took me about 10 to 15 minutes from putting the lock together to taking out the old deadbolt and installing this one.CHANGING COMBOI took it apart to change the combo, with my electric DeWalt driver, it took less than 30 seconds to take off. After deciding on a new combo it took about a minute or two to unscrew the back panel, hold the clear knob, swap out the tumbler pins, and screw the back panel back on.NOTE ABOUT COMBOThere are tumblers with red on top (coded), and others with blue on top (uncoded). The red coded tumblers make up the combo, the blue are non-combo pins (fillers). By default there are 4 red coded tumblers in the lock, but it comes with 1 extra red, and 2 extra blues, so you can have up to a 5 key combo which increases the number of guesses if someone started from the first option of 2 keys, or even the default 4 keys. So without purchasing new tumblers you can do a 2, 3, 4, or 5 key combo, so if someone didn't know how many keys you set they'd have to try all possiblities with 2 to 5 keys regardless of order. Like other reviewers mentioned, you don't have to have the exact sequence to get the combo, you just have to press all the keys in the combo (in any order) and turn thumb knob to open it. Still the likelihood of someone pressing all the keys would be pretty unlikely, not to mention I have a key on the door lever, so I have 2 levels of protection for those not motivated to get in. Below I put the possible combinations where order doesn't matter, so as you can see there's quite a few.You can also order more tumblers, but it seems like a waste after 6. Another reviewer/commenter mentioned you could drop the total guesses if you turned the thumb knob after each key press, so if you had a 5 key combo and they pressed all 5 key combos turning the thumb knob after each key press they only have 792 possibilities. Now I think this would require one motivated person, they'd probably be better served making noise and kicking in the door as it seems like a major hassle and they'd be seen as they went through each combo. It wouldn't be worth the risk since if they want my expensive tools they have to then break into my 5 foot gun safe, lol.# Poss Combos2 = 663 = 2204 = 4955 = 792 (total if turn knob after each press)Total = 15736 = 924 (total if turn knob after each press)Total = 2497 (if you ordered extra)Source: [...]FINAL THOUGHTSOverall I am very pleased with how easy the M210 is to install and used. I am also happy about not having a keyhole in it after seeing how easy it is to pick a key lock, and the electronic deadbolts all seem to have a backup keyhole which makes total sense because how else would you get it if it had no power (more for convenience)? These are the reasons I searched out and found the M210, and I will update my experience after I've used it for a while.Because I'm Sabbath observant, I required a non-electronic digital lock. This appeared to be exactly what I needed. And, in fact, it works perfectly. Its only design restriciton is that, like a conventional realtor's lockbox, numbers can be entered in any order and no numbers can be repeated (e.g., 1776). But, no complaint there. My problem is that LocKey USA has several versions of this lock and the instructions try to cover them all - with considerable confusion. Moreover, my kit claimed to have come with a "Bonus Mounting Plate", whatever that is. All I can tell you is that it would have been impossible to assemble the lock without any of the parts in the kit, except for 2 large neoprene pads - I never did figure out what those were for. I doubt that they were the "Bonus Mounting Plate". Another annoyance was that the last 2 screws I needed to assemble the inside toggle to the lock should have been two 1/2" round heads. Instead, all that remained were two 3/4" flat heads. The heads were too large to fit into the holes on the toggle plate so I had to grind them smaller, and I had to shorten them before the toggle plate would come flush to the door. No problem for me - I'm a machinist. but these issues would have been frustrating for many customers. The last word... the lock works great and I'm still happy with the purchase.Perfect for what we needed!My unit came with an extra red "code" pin which allowed me to increase the number of code digits to 5. That is, 5 out of 12 number would need to be guessed. Also, the number of combo digits would need to be guessed, which further expands the problem space and thus the inability for one to "crack the code". As others have mentioned, it actually does not matter what order you enter the numbers. You can even enter number simultaneously which I actually like. It makes it faster for me to enter the code; instead of 5 presses, I just do 3 -- two of the presses involve two simultaneous digits. If you want to calculate how difficult it would be to crack, you would consider this a combination (i.e. n-choose-k) as opposed to a permutation problem. Traditional keys can be bumped or picked, though there are now bump-proof locks. At the end of the day, all household door locks are deterrents. If one were determined to get into your home, he/she would simply kick the door in or break a window -- easy enough. You might be better off securing your high-value items in a safe that is bolted to the ground.This thing is made in Japan; it ain't cheap to manufacture there. I'm no metallurgist but I suspect that the machine screws are stainless steel. The bolt is machined brass. Build quality is amazing. Even the stamped parts are very precise. The word "digital" the is casted into the front is cheesy as hell but it is just an "engrish" moment IMO. In Japan, I'm sure they think it is cool. In the U.S., it just looks cheesy.You will be able to adjust the left- or right- handedness of the unit depending on how your door is hung. It will require unscrewing a few screw and moving a pin. They even provide you a pair of tweezers (also used to set the code pins).All internal components seem very well crafted. Yes, I said "crafted". This thing was most certainly required human hands to assemble. There are QA stamps and screws are color coded to aid in modifying the unit.no batteries required. purely mechanical.Possible downside for others....configuring the unit was somewhat involved. This is no plugin-n-play thing. It is no Apple product. I am an engineer by trade. Let's just say that I made a fantastic evening out of messing with this and figuring out how it all works. Not all will enjoy doing this. overall a fantastic product.