I got to try an Atari Flashback Portable tonight. The screen is way too small for my eyeballs. It would need to be the size of an iPad for me to use it, but then the screen would be too close for comfort. I think I'll stick with a TV many feet away.
I've only run into issues on a few games like Pac Man where flicker and small ghosts makes it hard to see well enough. But several others seem to do fine.