I'm curious (seriously, this isn't a snarky response) why not use the OEM Nikon GP1? Trust me, I've had at least 3-4 different GPS units and spent the cost of the GP1 several times over, so I am guilty myself of going down the 3rd party path only to end up OEM (it's sort of like tripods, I wish I wouldn't have cheaped out buying a dozen "cheap" tripods over the years just to realize I'd end up with a Gitzo anyway).
As I see it, the 3rd party alternatives offer a few features: 1. compass 2. Better display 3. Cheaper (?)
Is that pretty much it? I've struggled with several units over the last few years and the GP1 is the only one that just works with my D7000, D300, and D800E, including remote pass through.
I paid about 150 for my GP1 on Amazon. Seems on par with the alternatives. No?