Well, most multicarts, especially on the GBA are pirates and this compilation has Super Boy 4 in it, so it's related to some degree. And you're kinda in the wrong place to mention legality issues on a place that talk about bootlegs...I mean we do gray area stuff (dumping, hacking, etc.) with gray area games (unlicensed/booteg). I don't think it's a big deal personally.
On the note of the multicart itself, it's a nice selection of games, especially the MS port of Sonic Triple Trouble. Might get this on my flash cart if I ever get around to getting a MiniSD card for it, since I don't play Master System stuff that much.