It does exactly what it's made to do, which is emulate DS roms on the DS. It's extremely user friendly and easy understand, and being able to run microSDHC cards,(larger than 2GB,) is a major plus. Additionally, I tested and played through over 15 games on it, and it only glitched once, but I'm not even sure if lagging for two seconds really counts.
If I had to state a problem, it would be with the main website's software, which is an easy fix. It has trouble running certain large roms, but there are plenty custom-made firmwares floating around the internet you can experiment with.
In short, this is an extremely great value, especially for $10. Worth the buy.
*Note: Soft Reset is a big thing. If you don't know what that is, Google it.