Picking up a retroid for emulation

Anyone used one of these before? I've heard really good things. Mostly looking to emulate PS1, dreamcast, n64, and PS2 and from what I've read the retroid 4 does a solid job with all of them.

My main question is: how easy is it to get up and going with emulation on a dedicated handheld? I've done some really light emulation in the past, but only on pc and that was years ago.