I use Halifax and Santander apps in the UK. I think they are safe as far as data transfer.
While I prefer Santander bank, and it's app as a whole, I only have to input a 5 digit pin on a large number pad to open the app and the 1st stage 8 digit pin is clearly visible in a dull grey; so anyone overseeing that is a worry.
I prefer the Halifax log in where I have to enter 3 different letters of a 14 digit password, though that's obviously defeatable if someone could track every entry.
They have both recently increased security where I can no longer take a screenshot of my balance, (and hide my account # with an S-Pen), so that's a good thing.
I have not transferred money on an app, so I am not sure if there is another secure level.