Leakage is here indeed for 5V caps only.

Yes, it is a coarse way to measure Q, or rather compare Q, you find that methode on my side too, and also what the real Q was from the tested coils and that was way off but it is veryusefull if you have a spare transformer or choke. Both should give the same reading.

If you only have one, you do not know nothing because without knowing the inductance, frequency current and resistance you do know what the Q should be. But if Parker tells it is true it probably will be ;-) But do not forget, it is made for flybacks in televisions, those run on selfresonance and this orobably will work as the flybacks will problably all have a Q in the same ballpark.

But for other inuctors:

There is no such thing as an absolute High Q, like there is no such thing as an absolute high ESR. It is relative.

If Xc is 1 Ohm and ESR is 1 Ohm then D is 1, that is a really bad cap, if Xc is 100 Ohm and ESR is 1 Ohm then D is 0.01 and that is a good cap. But ESR is in both cases the same, and C can too, if F changes. If F is a contant then C is not the same, so 1 Ohm tells you nothing. You must calculate D from it and then you can say, good or bad. But if C is OK, ESR is low it is most tiimes Ok and if you calculate D a few times you get a feeling for what value is go/nogo.

About coils

If Xl is 100 Ohm and Rs is 1 Ohm then Q is 100, rather good, but if Xl is 1 Ohm and Rs is 1 Ohm, Q is 1, an inductor with a big loss. But this can be the same inductor on an other frequency or an other inductor on the same frequency, or the same inductor, on the same frequency with shorted windings and there for a lower selfinductance and lower Xl. But without a reference you do not know.

I needed a choke for a desing I'm working on. It had to be around 80 uH upto 500 KHz. The first one I made was 88 at 5KHz and 0,6 Ohm, but at 500KHz selfinductance dropped to 43 uH and Rs was 24 Ohm. ( core loss, not a shorted coil) The final coil was 86 to 82 uH over this range and Rs from 0.8 to 2.8 Ohm.