Signed up today and then found that I could not log back into the app on my iPhone 4 (yes, I know) running iOS 9.3.5 at first. When I tapped the app the passcode screen appeared but then so did the keyboard, which I could not get rid of. I tried coming out and going back in several times, with the same result, viz that the keyboard prevented me entering the passcode.
I tried again half an hour later and this time I got passcode screen and no keyboard, as required. It all seems fine now, except that I am concerned that the problem could or might re-occur at some point when it mattered, since there seems to be no other way to monitor or manage one’s account (whereas with, say, Monzo, one can access via iPad too).
My family and I are aiming to trial and compare Revolut and Monzo until Christmas and the select one and abandon the other. Revolut is winning on card colour. Delivery of Monzo card is free though even if one has to wait weeks because of the 38,000 queue.