I got a BT-5 from Unitraq a couple weeks back and I"m very happy with it. I've not had any previous experience with GPS to compare it to but it seems to work very well with Mapper. It does occasionally fail to get a fix but a quick power cycle of the receiver solves that problem.

The only thing I dislike about the BT-5 is that the casing seems to not do well with heat. I left it sitting on the dashboard of my car one hot afternoon and it warped and shrunk.