G Tech Pro Rr Meter

Does any body know if the G TECH PRO RR METER or any other meters by g tech are accurate or not? They say you only have to plug it into a cigarette lighter and it starts to work as soon as the car is on. That seems like a weird way to measure performace. They also say it can find the dyno graphs and get the optimal shiftpoint down(with the new RR meter). So basically are these things worth it? It'd really suck to waste like 350 on these and have them just shoot bullshit out.