I can personally attest to the accuracy of the GPS on iHike when used on an Apple iPhone 6S. It is spot-on. But I imagine that the antennas vary from one type of phone to another.
And you don't need line of sight -- I have seen iHike work in the bottom of a canyon and in a deep forest. Not sure if it would work in a cave, though.
But -- and this is critical -- iHike does not pre-load all of North America. You have to decide where you are going to go and then select the topo quadrants for that area. This has to be done where you have cell service. Selecting and uploading is really easy.
So then, with the topos in memory, you can now travel off the grid. But if you decide to alter your route into an area that you have not pre-selected and pre-loaded, you are out of luck.
This rarely happens to us when hiking, because we hike slowly. In a car, though, you will be zooming across the topo quadrants and can easily travel into terra incognita, so to speak.
So that is a big difference between iHike and the Garmin systems. Not a deal killer, but not a trivial issue, either.
