One I use (PS2 to HDMI) works great, and it was quite cheap. I bought it once I saw video with cheap updates to PS2 without modding, and I did it. Large capacity SATA drive in PS2 with boot from memory stick which is surprisingly very fast. Loaded all of my PS2 collection on device and played it only couple of times since then.
I actually tried more PS2 games on with recent PS2 emulator update + Launchbox.
Same with PS1. It is in basement connected to an old TV (still flat, 720p iirc), but mostly I play all PS1 games on emualtors now. Lame old game who needs save state and some cheats so that I can beat game without grind or hours spend to discover all hidden treasures...
Same goes with N64, xBox (original) that are all connected to the same old TV. Another xBox original is connected to larger HD screen, and both are loaded with some xbox emulators, but rarely I start any of them...