Jury's still out. Crew used it at an ECR enduro and loved it. We tried to use it at Daytona, but it wouldn't work. Other tracks don't implement the system, and it's useless. Memphis doesn't use it, and our lone crewman gave up trying to time five cars in a class, sat back and enjoyed the race.
I think that when it works, it's great, but you have to be in the proper place, at the proper time to receive the signal. And, of course, they have to broadcast it.
One thing's for certain...it is the official time regardless of what your wife says. AMB's not infallible, but it's pretty dang good!