That device has been discussed in the forums before, first in 2017 when they launched their indiegogo campaign. 
See the existing thread (The topic title is a clickable link)
As I said two years ago, they do have a patent which is interesting. I agree that they seem expensive in terms of the actual value being delivered, plus, as @Ryan780 said, The requirement that each participant carry a phone with them. So interesting technology, but I’m not signing up to buy one.