I have owned two First Watt amps, the M2 and the Sit-3. I would like to hear an F8. Agree that the 6moons review goes into great detail and does a nice job comparing several models. Of the two, the M2 had a bit more power (25 watts into 8 ohms) vs 18 into 8 ohms for the sit-3. I preferred the M2 to my Rogue Stereo 100 amp, despite the rogue having much more power. Better soundstage and detail. So I sold the rogue amp.
I then got a sit-3 and thought it was again a bit more detailed with a larger soundstage. I recently got some caintuck open baffle speakers, and in my small room (11x 14), the Sit-3 and the open baffles sound phenomenal, with jazz, folk, rock, piano music, ambient… I think the sit-3 sounded better with the open baffles (94 dB sensitivity) than my ported bookshelf speakers (87 dB sensitivity), so they may do better with higher sensitivity speakers.
i sold the M2s and kept the sit-3. Hope this helps