Not sure how the cart works exactly, the roms may be modified on a case by case basis to insert the snippet of code that allows you to reset the game by holding start. Pure speculation on my part, really, though this could explain some of the sound being a bit screwy. For me, this is particularly noticeable on samurai showdown 2 where the intro music after the neogeo logo is way off.
Also if you leave it on the game select menu too long, terry's white shirt starts to do some serious burnin on my monitor - a grey blob stays on the screen where his shirt was before once the game has started.
Other than that, it has a really good selection of games, would definitely buy the next version if it comes with windjammers, which is sorely missed.
Edit: This is the 161 in 1 cart I'm referencing, I haven't used the others though I'm lead to believe they're very similar.