I have exactly the same as referred to by GtE. It works well, yet would work better if I could spare the time and effort to get it properly adjusted. Have you tried any adjustment on yours?
I'd be happy to receive some guidelines to this adjustment: I imagine one could do the "course" part on the ground, rotating the plane by steps of 30 or 45 degrees and adjusting until it reads ok; then confirm in flight by checking against GPS? I should think the first part can easily take two or three rounds... Is there a published procedure, somewhere?