I haven't used the Solmeta solution, but it does seem to be more popular than Nikon's GP-1A. I haven't pulled the trigger on one yet, instead I'm using a smartphone app to capture coordinates that I later add to the images via LightRoom in post.
I've heard that the GP-1A negatively impacts camera battery life in two ways ... one, it depends on the camera body for power, so it's leaching power from the camera's battery when it's on. Two, because the GP-1A takes so long to acquire a GPS lock, it encourages you to disable letting your camera sleep to save power ... consequently both the GP-1A and the camera are using more power than they need to all of the time.