I've only had 2 complaints with gen_statem, the docs were initially some of the most confusing/unclear and the state_functions callback mode (which I think partially is to blame for my first complaint as I was expecting a more gen_server like api with handle_* functions -- which exists but the docs use the state_functions for most of the examples and the handle_event just kinda getting some "oh by the way this exists" examples). I actually initially decided to just keep using gen_server's with a "status" or whatever value in their state as I figured it was good enough. At some point over the next few weeks I actually ended up having this talk[1] pop up in the recommend videos, and I figured I give it a watch to see if it would help make sense of gen_statem or at least just confirm that I don't need it. And while watching it, once he started explaining actions (timeouts, state_timeouts, postponing, etc) I realized that gen_statem literally solves so many problems that I've had in the back of my mind on the project I was working on like "I should figure out a way to change the state of A and do something when it doesn't receive any messages from X,Y,Z processes" (gen_statem's timeouts!) or "how should I handle messages received while attempting to recover, I guess I could put them in a queue or something..." (oh, gen_statem will let me postpone them until it's healthy!). It took a couple more re-readthroughs of the docs to fully grasp, but now it gets included in almost everything I work on, it's so useful (though I guess I should've assumed those were already solved problems by the BEAM/OTP as usual).

However, now my biggest complaint about Elixir is that gen_statem didn't get any official wrapper. StateServer looks like almost exactly what I would want out of an official Elixir wrapper. I also like to see the addition of `handle_continue` as well, because the first thing I did before migrating any of the gen_server's to gen_statem's was create a small wrapper module to a) make the handle_* return values more in like with GenServer's (basically just making it {:(no)reply, (transition|keep), data, [actions]}) and b) add a quick and dirty handle_continue callback because I use it all the time with GenServer. And this literally just looks like a more polished version of that, so thanks!

[1] https://www.youtube.com/watch?v=_4MTIffWhYI