I haven't used them, but I've seen them up close. The 12'x16' frame at Tallon Lumber in Canaan, CT is about 20 minutes from me. The finished product looks ok, but it is very obvious that it is not mortises.
I personally feel that you can mortise and tenon a frame faster and cheaper than you can do it with fasteners. Let's compare a post to tie beam joint. A tenon on an 8"x10" tie beam with square rule reduction and a through tenon on an 8"x8" post, with peg holes, might take an hour. How long will it take, and what special tools are required, to use the T Rex connectors? You still have to accurately cut, slot, and drill the timbers, then you have to pay for the hardware on top of your time investment. I would very closely investigate the time and expense of using a metal fastening system.