The GPS was an iphone, the iphone battery died just before it hit the ground due to it succumbing from cold but its last location (they had it in real time) and a large LED light attached to it helped the father and son find it
“I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.” Stephen Roberts
in his responses on the vimeo page he says it was a GoPro HD
as for legality and such, he also goes on to say that he had to contact the FAA among other government folks to let them know when he was launching and what he was planning because it had to meet a certain weather balloon spec.