the t100 and t200 are the ones most commonly used. ive only used the t200 (downloadable) and has been great. until i fell off at donington and broke into a million pieces! most uk circuits have the beacon that will get picked up. although they are not allowed on trackdays. i definitely wouldnt use one on a trackday, oh no, definitely wouldn't tuck it away somewhere on the bike, no, definitely not use one REALLY REALLY carefully so no one see's it.