Trimble Outdoors and Backpacker have had for a while the GPS Pro App and I have tried it The features and benefits of a layered map out performs Garmin's mapping GPS for weight and size. The screens are easier to read and larger, great in bright sunlight and although there's less infomation - like "time to destination" or "anchor alarm" the missing details are easy to find with other apps. I am still fuzzy on how to load your own route - but to see a topo layer and have a satellite layer is awesome..... great for when you are off trail!
One clear disadvantage - paying $1-3 for tracks from others - I have compensated a little for this - Yahoo/Google Earth - has all the bike/rail to trails stored in the bottom layer for free.
What have you found so far? - Like's and dislikes... wide open here.