Pros: My son has used this with both an R4 and an Acekard 2i. Works well on both. It's too bad the microphone doesn't work on his DS Lite as the guitar hero (downloaded - does not come with package for those who might assume so) requires the microphone use for a portion of the training. Due to this, this device has not been used to its maximum but this is a fault on our end, not the products.
Cons: A little hard to slide into the Ds Lite slot. Instead of dealing with this, my son just leaves it plugged in at all times.
Other Thoughts: Have not had the "stuck button" problem some others were/are having but then again we don't use this controller often due to the microphone issue.
I will say though that this is a great way to develop carpal tunnel - your wrist/hand will hurt after long continuous play, but that's with any controller, not just this one.
Bottomline: If you have a DS cart and downloaded the game, this is worth the $8.