Very cool idea. What's the range of BLE connectivity? I can't imagine it gets far

It's not long range by any stretch. The use case is more "my group split up on a trail and I want to know which fork they took" vs "track someone across a mountain." The ghost marker system helps here too. If someone walks out of range, their last known position and direction stays on your map, so you at least know where they're heading and how long ago they traveled that direction.