Please don't waste your money on any 3DS flashcart. Gateway 3DS hasn't updated in 2 years and the team has since abandoned the cart for Stargate3DS (which they also abandoned right after the release.) It's honestly cheaper to buy a larger microSD card than it is to buy a Gateway 3DS, which is what I recommend doing.
Realistically what you said is counterintuitive. You still have to go through the same process of finding .3DS roms as you would to get .CIA ROMs. You are going to to have to get them from the same source regardless.
A flashcart isn't worth it because all of them haven't updated to worth the price tag added on them. Whereas you can get a microSD for the same price (often cheaper) and accomplish the same results, but with better support.