Trimble may have fixed the problem, but when I evaluated it, the logic was OK until you went to change the transition points on a GPS approach. If memory serves me right - upper line controlled by outer knob, lower line by inner knob - until you got to the point of having selected the runway (upper line) and trying to select a different transition than the one displayed - the inner knob merely stepped you through the waypoints on the approach. If you wanted to change the transition, you had to press a button (ENT?) first - completely counter-intuitive and flummoxed a whole lot of people.
Transport Canada said it wasn't suitable for IFR until this got changed, among other things.
Loads of other things as well, probably fixed at the time, but the KLN-89 and 90 were way ahead with their very small moving map displays.