I'm not sure why this topic is being posted in the DSTT section, but the Acekard 2 is one of the best carts in its price range (it's much nicer than the DSTT and is worth the additional few dollars in cost over the DSTT).
The Acekard 2's menu system is one of the nicest and most responsive (which in my opinion is the most important thing about a flash cart after compatibility). Most users won't ever use features like game state dumps (RTS) and slow-motion, but if you feel those features are worth paying more for, you might consider a cart like the CycloDS.
One advantage of the Acekard is that Acekard has released source code for the menu system of the Acekard 2 to a few people (Normmatt, Smiths, Gelu, and a few others) who had been customizing the open-source menu for their Acekard RPG cart, and the result is several custom menus for the Acekard 2 that add significant features to the official menu. Normmatt programmed slow-motion, which although hasn't been added to his custom menu (because it requires modifying the code each time Acekard comes out with an official release), may find its way into the official firmware at some point in the future. Acekard has indicated that it plans to incorporate many of the enhancements made for the custom menus into the official menu.
As Destructobot indicated, the new beta firmware does seem to fix the speed problems with slow memory cards. And yes there were a couple of bad batches of Acekard 2's where about 10% - 15% of the carts from those batches were bad, but the latest batches of AK2's have reportedly had few if any returns. So Acekard apparently corrected the hardware problems they were having.
-Bri