Have had a few problems with my iZettle 2.
Main problem seems to be when I load the app onto the phone.
It takes a few seconds for the message to appear on the phone saying the bluetooth connection has been made with the card reader.
But if you start the process before the connection message appears then the whole thing seems to go haywire, and it won't connect unless you close the app down and start from scratch, which can take a while.
So the way round this is to wait until the connection message appears before keying in the £figures, but this can take a few seconds, which seems like an eternity if it's a half-mile job with some noisy students, say.
So in the rush to get it done and dusted I've often keyed the £figures in before it says it's connected, which just ends up making everything a whole lot worse
