I think the HHT is valuable, as long as it is calibrated to a known hair with a known result. I use my wife's hair, she has thick long straight hair, I know the razor is sharp enough to shave with when it passes the HHT at a 3 or above. The HHT says NOTHING about how smooth the shave is going to be. For me I can get HHT'5 in the 4-5 range with a Naniwa 12K followed by CBN sprays, but it is a harsh shave.
http://www.youtube.com/watch?v=W1hAm3WogU8
Again for ME, the HHT is a measure of how sharp the blade is, says NOTHING about the smoothness.
I have read many people say they get great shaves from a razor the fails the HHT, I would love to try one of those razors because I have a hard time believing it.