I too am a long-time purchased "pro" user, and just discovered all of this last night. I use the app maybe once a month, either when I'm outside (to turn on lighting) or just too lazy to get up off the couch(!). The app worked well, now it crashes when I simply try and select a thermostat.
Judging from the lack of complaints on this forum (why aren't there 50 people complaining? Ok, why not even 20 people complaining?), it looks like the app isn't in high demand. I'm sure app revenue is slim to none.
At the same time, we do have to recognize that as Android OS versions progress, the app will need some attention to keep it functioning. I think a reasonable annual donation would be understood by most users, say $20. We, as users, have to hope there are enough $20 donations to make it worth it to the developer for his effort; or the app will simply die.
I would like to see the developer's thoughts/response to all of this. I enjoyed the app, it worked well - and I thank him for that.