I’ve never used a transponder but the track I’ll be racing on says that 2-wire, 3-wire, MRT, and amb-RC can be used. Looks like the MRT transponders are the cheapest so that explains why it would be good to consider them. The 2-wire and 3-wire are about $20 more from what I can see.
The 2-wire and 3-wire appear to be called MyLaps which connects to an app named Speedhive. I believe that’s what is used at the track where I’ll be racing. I’m not 100% sure how they work but I’ll learn more hopefully tomorrow at practice.