I thought it was fine on Android, I played many games on it that worked well even on those old underpowered phones. It was never good, but probably about 0% of flash apps were written that targeted mobile so I wouldn't have the expectation of good.

I think "fine" is being generous.

When it worked it was... not great, due to UI issues, but it at least worked.

Trouble is it seemed to not consistently work. I worked at a flash game developer at the time (Zynga) and it would not always load our games even if it had done so previously - the difference was sometimes just refreshing a page.