Until recently SuperCards were very reliable. And contrary to what many people think, most games are not slow. In fact very few games have a slow down problem that effects play. Also SuperCard team still supports their product, but have heard EZFlash does not.
I have had about 8 SuperCards go through my hand, and all but the 1st eventually broke. There are discussions about this elsewhere, but suffice it to say, the broke ones mostly came from DealExtreme a few months ago, and they don't sell them any more. I ordered 2 more elsewhere, and will have to see if they are good. But my original SuperCard still works wonderfully!
However, if you play the few games that are slow, it may leave a bad taste in your mouth, and thus some people give sour reviews of the unit. The price is very cheap, and if you get a good one and don't care about the very few games it won't play, this is the card for you.