I had about two dozen of Garmin devices in my practice. So I can make make conclusions.

1) Any maps (not only Garmin) have a very irregular accuracy. For this there are many objective reasons that are caused by the production technology maps. So very often accuracy of map wants to be better.
2) Year after year, the manufacturers (not only Garmin) has changed the approach to the devices. In the beginning it was so-called "military" stile - professional equipment in high cost segment. Now we have come to consumer electronics in average cost segment. As a result we have a very quick acquisition of satellites and a glossy interface but we loose a stability and a reliability. The future scares me is the new trend of store from low cost segment - it is playthings made in China So no reasons to expect from new models the superior performance. But the latter is in the assortment in high cost segment again and is designed for professionals.