I build a simple Pacman game. Running on Android wasn't a problem even though the builds took an entire minute to complete.

Compiling and running on iPhone was a nightmare though: At the beginning of the project I was able to run it - some days later I had to tweak the RAM being allocated to the trans/com/whatever-piler - a week later and the weeks after I was unable to compile it at all, there just wasn't enough in my MacBook to throw at the thing.

And the subjective performance was relatively bad too. They tried to reimplement Material Design and it looks somewhat like it, but it performs pretty badly.

Even their own conference app demoing Gluon Mobile is terrible and that says a lot.