Are they even bad with pokemon?
I'm not a fan of pokemon so cant say I tried it. I've still got the cart somewhere, if it would be helpful I could test a game or 2 vs the ez-flash iv (as I dont know how the pokemon games are meant to run )
I recall trying a couple of the mario games, mariokart, sonic, max payne, mario vs DK and probably a few others. Mario vs DK was pretty playable (although not perfect) but all the others were horrible.
Personally I'd say avoid unless you dont mind spending the money on something you very likely wont use. Now that the EZ-flash carts are hard to find it doesn't make it easy I know, but if you can hold out and keep looking for one I think you'll be happier in the end.
Really they are an option of last resort. Like FAST6191 said, even when the supercards were new they were really only good for playing DS ROMs when used with a passme (as that didnt require the cart to provide the data as fast/with as accurate timing).