Since he's planning on buying a flashcart, he wouldn't need one, anyway. As for the cartridge itself, I'd recommend the more expensive Mega Everdrive. It has more features, including real-time save capability, which is perfect for all of those old action games which don't support saving at all.
If you're looking for something on a cheaper side, you could always take a look around AliExpress. They're selling Everdrive clones, though they're almost as expensive as the genuine product, so it's up to you to decide whether or not it's worth the risk.
Also, keep in mind that there are many Genesis clones out there, including those two-in-one and three-in-one combos, which let you play Super Nintendo and NES games as well. You won't be able to connect a 32X or a Sega CD, but it all depends on what you're looking for. Since you don't seem to care about original games, you might as well get a combo console and get a flashcart for the SNES as well. The good ones, like Everdrive, work with the clones just fine.