Personal transponders

[HOTSHOT III]

I'm starting to race at a few different tracks that all use the AMB timing system and would be interested to hear people's views on whether the AMB or MRT PTX is the better option.

I race 1/10th and 1/8th buggies so ideally i'd want one for each car. I've noticed some people on ebay are offering paired MRT ones with the same number, is this so you only have to remember one number wherever/whatever class you race in?

Is there definitely only one type of AMB timing system, and only one type of AMB/MRT personal transponder?

Also if any one could post some links on here for each type that would help as i've tried searching online and haven't got very far. Thanks for all your help!!