I have used it. GLSDA (Banner on the gun forum) is currently doing research projects with it, so I don't want to say too much to take away from the write ups that they will do.
But, I will say that it is cool as a training tool. The reason is because it inspires you to hit harder with your pad work because you want to try to beat your last "score" so to speak.
As far as a tool to accurately measure the trauma potential for strikes, I am not sure that it is that accurate.
First off, it measures G force, not force per area (square inch). Truama potential of strikes has just as much to do with (if not more to do with) force per spuare inch as it does G force. Plus G force can be effected by the type of bag you attach it too, how and much swing the bag has, as well as many other variables. So, a push hit with a palm could register more then a hit with a stick, for example, even though the hit with the stick creates more trauma due to a high force of impact per area. So, it is difficult to get an accurate reading of how hard one is actually hitting. You won't get a very good comparison between individuals (meaning, who hits harder, this guy or that guy) or between strikes (like palm vs. punch), and there are too many variables as far as it goes for getting an accurate reading.
However, as a training tool it isn't too bad, just as long as your going for a comparison of data (meaning, did I hit with more G force this time vs. last time) rather then completely accurate information.
Paul