Not bad at all. – StoneX iBroker Review

Pros: All the expected functionality is there and working. The charts are quite good. Cons: Charts take a while to load. The chart trading is good, but be prepared for a few seconds of lag. It is sorely lacking a way to enter OCO orders. Minor stuff: Switching to another app and back, or even an incoming phone call, causes the app to lose its connection to the mother ship. Usually it re-logs-in in a few seconds, but don't plan to switch back and forth with a calculator app. Also, switching to paper trading and back requires you to re-enter both passwords, making that impractical to do frequently too. The phone (as opposed to tablet) version doesn’t let you see contract details or trading hours if you have an open position. Overall: Better than most bespoke brokerage apps.
Review by @marshray on StoneX iBroker.