I was looking for a combination lock not only to eliminate the need to carry a key, but also to help deter typical thief who is well familiar with how to defeat a typical lock. I did not want the lock to be key enables even as a back up. This unit was the answer. This lock is not a digital lock, it is completely mechanical. has a nice built to it. I took my time on the installation which took about 45 min. changing the combination is straight forward if you read and follow the instructions. you unscrew four screw in the back of the keypad, press and keep the C button down, then with the provided tweezer you remove and replace some red pins with some blue pins. Order of the digits does not matter with this lock. the provided pins allowed me to set a 6 digit combination. the instructions talked about a 7 Didit combination but there were not enough red pins in the box to do that. you can go down to a 3 or 4 digit combination if I am not mistaken. In theory, it is possible for someone to use a brute force method an by trying all the possible combinations ultimately open the lock. but It would take that person more than a couple of hours to do that. This is not a super high security lock anyways (most locks are not). There are easier/faster ways to defeat this lock than to try all of its possible combinations. I can think of one way, but I am not gonna share it online. I think this is great for low security areas (e,g, installed on a door to the pool area where the combination could be shared with all the tenants in the building), or when you need a lock that does not have a key. I like the fact that this is not Digital/electronic. I read a lot of review about those and they seem to be too complicated, too expensive, and things can go wrong with them like all other electronics (too complex of a unit has too many points of failure). the first time I installed this lock, I realized it unlocks the door without combination but would require the combination to unlock the door. a quick look a the documentation and I realized I have the lock set of a left hand door and I need to change it to a right hand door. Two small blue screws in the back of the luck gives you access to a small pin. you take the pin out of left hole and put it on the right hole and voila, you got yourself a lock for a right hand door. I am a very handy person and I have all sorts of tools. I rate the install at moderate as I had to make some other minor adjustments to the door to make it work. if you are not handy with tools and locks, I recommend you hire a locksmith for the install. This lock also required drilling an 8mm hole in my door which is not ideal. but it looks, works, and feels fine and that is all that matters.