I've had zero issues with any PS1 games that I've thrown at TS. There's actually a fast PS1 core that comes with it. That's what I use, as it plays everything @full speed.
And I agree, the Funkey S is way too small to play anything. I rarely play mine these days.
The problem is retro gaming will cease to move forward, because the past consoles like PS3, PS4, or Nintendo Wii U will always have amazing graphics, which means they'll never look old or retro.