This was a Christmas gift for my daughter, she has yet to use it, don't know when she will.
I have only used this once so far for a long ride (140 km). It worked very well with no issues. It does the job an definitely better than carrying full extra bottles inside your jersey's back pocket. It would be perfect if it had a clip/hoop/surface to which you could attach your rear lights.
Easy to install, relatively lightweight but sturdy (although yet to ride with it) and two decent sized bottles. Highly recommend!