https://m.youtube.com/watch?v=H113JRugBR0
It's certainly no worse than any of the cheap Chinese emulator handhelds people are buying on eBay, once you adjust the settings according to your phones performance.
On my phone, I got a 4" 4:3 screen which feels a lot more civilized to play on than the 3" on my 156 in 1 Genesis arcade thing. I don't even mind the 16:9 screen with 4:3 content because it's an OLED screen so the borders at the sides are completely black:
I tested it with a $10 Bluetooth gamepad off eBay. It's essentially a PlayStation pad clone. It's not great but it works well enough for this purpose.
Who would have thought that you could one day play Neo Geo games on your phone...