I had my first working system that I felt confident enough in to share with my neighbors - I emailed the tenant mailing list and offered to set it up for a few people without any charge except for the Raspberry Pi 3 hardware (~ 80€ at the time).

I got multiple requests and set up 10 apartments in 2019. In the 5 years to come, some of them have sold their apartments or no longer needed remote access but all other deployments are still working well still on their original SD cards.

I think the technical reasons for the successful setup were:

• I disabled as much logging as I could to reduce SD card wear - apache2, cronjobs,...
• Before I offered my solution to others I thoroughly tested the whole thing and left it running for a time to see how stable it is
• I expected most if not all neighbors would have dynamic IPs provided by their ISPs so I installed a dynamic DNS service to keep them up to date
• I am able to access each RPi via SSH tunneling via the internal building's LAN so any house calls were reduced to the minimum
• I documented everything well and made my findings public for all to use
• The PLCs themselves are actually very stable, same goes for the python HTTP-to-UDP service

The biggest issues I noticed and fixed during these years were:

• Random Wi-Fi hardware/driver crashes on the RPi 3s I deployed - a few of the devices never crashed, some crash once per year requiring a reboot and 1 device crashed every week which I solved by using a USB ethernet adapter to add a second ethernet port.
• Apartment owners changing internet providers - this is usually the only time I need to do some maintenance and it usually requires configuring the new "modem" the ISP provided: I check for local IP conflicts and set up port forwarding again.

This first public release offered the following 2 remote control clients:

• The exact same Android app as on the apartment wall-mounted tablet
• A web interface built using the Django CMS the way the smart apartment vendor envisioned it - this can be used on any mobile device or computer

But I couldn't very well leave it alone at that, could I? :)