the 520 had better buttons. I bought the 530 a few months after it was introduced, and returned the first one because one (and only one) of the buttons was soft (no feedback when pushing it) and it did not register all presses.
The buttons on my replacement 530 has been good. Not great, but good. I have thought about the 830, but can’t be bothered as the 530 is working well.
DCRainmaker review from 2 years ago:
Review: Garmin Edge 830 Cycling GPS In-Depth Review | DC Rainmaker