I have several.
They are great units.  Easy to use and fun as well.
They are stable and run the best using MultiMiner with the BFGMiner dualminer pre-release.
I even did a review of them you can see here.
http://www.cryptocoinsnews.com/news/dualminer-sha-256-scrypt-usb-miner/2014/02/26
The people from DualMiner are great to talk  to and very responsive if you have questions.
I hope this helps you out.
Happy Mining.