I bought it direct, although in all honesty I didn't even check here.
The only issue I've had is with real thin poly it can slip in the gripper. But I've had that problem with practically any gripper I've used (a little sandpaper rub & it's all good).
I took it on faith that it was calibrated, but RacquetTune measurements have been pretty close.
I really don't worry about the actual number, just that it is consistent. And so far, it's been dead on every time.
"Nobody beats Vitas Gerulaitis 17 times in a row" -- Vitas Gerulaitis, after beating Jimmy Connors on his 17th try.