Leaning towards a fi. The NordPaw is hideous and looks like a toy HAL9000. The Tractive is very large and that defeats the stealthy purpose I would like it to have. If my dog gets stolen, a fi might not give itself away as a tracker. And fi offers a ton of third party collars. I wish the unit could be clipped to an existing collar, as I just bought one that looks great and has Mia's name and my phone number on the buckle.
https://shop.tryfi.com/accessories