EZ-Flash IV has always been the go to for GBA, but it's still very chink-y. there's the EZ Flash 3-in-1 too but that's more of a DS Lite expansion than anything. Unfortunately he had to get it into a big cart so it won't fit like a normal GBA cart but I'll still probably wind up getting one, probably after a second rev comes out because let's face it, it's gonna happen.
I don't see Krikkz working on the DS though, DS Flash carts are as plentiful as the sea is wet. FYI If you want a good DS Flash Cart, get the R4i Gold RTS, it uses the best cart firmware and supports Black 2/White 2, it's only $20. Avoid the SDHC-Dual Core ones, their firmware is shit. If you want to go all out, you can get a Supercard for like $40 but the only advantages to it are the SNES and GBA emulator which are easily outdone if you're playing on a 3ds anyways (I wouldn't recommend it though, at least on the XL it looks like pure shit playing DS on 3ds).
If you live in the US, the best retailer for those is modchipsdirect.com, they're one of the last few based in the USA and shipping from USA.
