I sprang for the Supercard DSTWO+.
I could give an in-depth review, but here's the rundown of what I liked and didn't like (and didn't try)
Pros:
-Card has good build quality compared to Action Replay DSi (not hard to beat) but is much worse quality than a retail game cartridge.
-Everything is on the microSD, so no need to worry about gamecard firmwares not being able to update due to your DS not working
-Onboard processor allows for more advanced features, like game slowmo/speedup as well as cheat code creation
Cons:
-Drains the battery faster even when not in use
-Processor is covered by only the sticker, so better hope it doesnt come off.
-Cartridge is noticeably larger than a normal cartridge and can get stuck in the gamecard slot if not inserted properly
-microSD card has a tendency to get stuck inside the flashcart. I ALWAYS have to pry it out. No damage to the flashcart so far, but avoid inserting and removing it too much.
-microSD card is absolutely required to use the flashcart, and is not included
Overall I'd recommend. It's lasted quite some time and has served me well. It pairs very nicely with a class 10 16/32gb microSD. That lets it fit a few hundred DS games (assuming you aren't just putting a lot of copies of B/W2, which are 512MB each) with saving and loading in games taking noticeably less time. The creators also stand behind their card very well and I don't expect support to be dropped in the near future.
I ordered from modchipsdirect, average service (about 5 days from order > arrival).