jonnyk, we actually talked about this point in the other, longer thread. In a nutshell, I agreed that we don't know which is accurate, but that's the problem. Tools that measure the same item should get the same results.
turbolx also mentioned that the Mustang Dyno uses strain gauges and the DynoJet uses a known mass which essentially makes a DynoJet more like a balance and a Mustang Dyno more like a scale. I do think that it would be optimal if the DynoJet had a known mass that was the same mass as the vehicle you are testing.
You can read more about this in the other thread.
Just so you know, I have an e-mail into MustangDyne.com to see if there are any nearby since I plan to use one if they are. Not to get a HP reading, but for tuning purposes.
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351W 89 Mustang GT Convertible