As you see experiences differ from person to person
Your primary problem was the system being off-line and as such guests trying to solve the problem on their own (without of course knowing that they are helpless). And an offline system is a HUGE pain in the … But you see, it was one problem leading to another: system offline -> guest trying to be smart instead of just reaching out to you. This pattern is inevitable: whatever reason -> guest will try to be smart
I can even imagine that there are two versions of the Nuki app, say Nuki Guest and Nuki Owner and some “intelligent” fellow, seeing that the Nuki Guest is not working will install the Nuki Owner version. Who could stop him? And if we follow the logic: AirBNB generates a key for each guest, but guests rarely redeem all of them, so there would be probably keys available for that person to import into Nuki Owner and look around. What i am trying to say is that there is a gazillion of possibilities. But as long as the guest imported the key, arrives at the door, opens Nuki app, smart lock is available, can click on the damn circle, choose unlock and the door actually unlocks i am convinced that 99% of guests won’t ever try and see what else the app can do.
Don’t get me wrong, i am not against a light version, by no means. But there are so many other really bothering issues and Nuki has just a limited set of developers that i would rather them spend time on those and fix them than try to create a different version of a thing that exists already.
Regarding the setting of the PIN. Nuki team, make it mandatory! There should be no smart lock that is unprotected by PIN! It’s not something an owner should do if he/she wants, an owner has to do it, it’s compulsory and non-negotiable, period. When you get a device (debit/credit card) from your bank that basically is a door to a form of your assets (money) do they let you get away without setting a PIN? Do they tell you “please set a PIN, but only if you want to”? Would any sane person, even if given the possibility, walk around in this world with a card that has no PIN? Don’t think so. Then why aren’t you applying the same rule to a different device (smart lock) that protects a different, yet much more valuable asset (your home)? Oh, i know, because people are lazy, don’t know, don’t read, don’t care, don’t realize the implications etc. Because technology has become so available and easy to use that people think they can handle it always and they know better. Well then make them! When setting up the smart lock make a compulsory step where the person HAS TO put a PIN. Problem solved. And i bet you it will feel natural to everybody and nobody will complain, just as nobody complains when they set their PIN on their debit/credit cards. And if anybody complains they should just stick to the good old physical key because it means they are not mentally ready to use technology for such a serious purpose.
Guests will always have some issues, problems, what not. But i repeat: rather the enrollment process should be somehow simplified because once the guest installed the app and redeemed the code and as long as when they arrive to the place they can open the door easily and on the first try they will be happy and 99% of them won’t give a rats arse about what hidden settings the app might have.