I have both a DSTT and an Acekard 2. The Acekard 2 is well worth the extra few dollars. The DSTT lacks some of the most basic features that nearly every other flash cart has, including the ability to list games alphabetically (yes, they appear in the menu in whatever order they happen to be in the file table), the ability to view folders (all .nds files on the microSD card appear in one long list), the ability to load GBA games to a slot 2 cart automatically, the ability to switch skins from the menu (only one skin is supported -- to change skins you have to replace it with another skin on the microSD card), etc. In addition, the menu is sluggish, a large number have hardware problems, and compatibility updates are few and far between (much less additional features or bug fixes) because there are a huge number of clones so the DSTT team spends much of its time developing fake-killer firmware rather than updating the menu.
-Bri