Bought a handful to try:
Nukeproof Enduro* - Initial bite not as sharp as the stock metal pads. Hold is *slightly* better than the stock metal pads. Lever feel is a bit spongy compared to other pads.
RWD Organic - Currently bedding them in. Not impressed so far. Will update after a few rides.
A2Z Organic (blue) - Initial bite not as sharp as the stock metal pads. The hold is much better than the other pads I have tried, including stock metal and resin pads. I would recommend these.
Superstar Organics - Pretty poor bite compared to stock metal pads. Hold was no better than stock metal pads.
Nukeproof DH - Haven't tried them yet.
I have five unused Superstar Vibe rotors to test with, one for each pad. Bedding in consists of sprinting and braking. Letting them cool down completely when they are HOT.
* Found out they don't make the Nukeproof Trial pads for the M640/M810/M820 anymore.