Love my FirstWatt F1 with my Common Sense Audio 12" drivers. Easily best match I've found for the sound I am looking for (detailed, driven, and with great dynamics and PRaT). F1 is also a fave of Ed shilling for his Horn Shoppe horns. Great detail and dynamics. Will also be comparing it to a DIY F2 shortly. I'll try to remember to post my impressions here.
The 6moons reviews of the FirstWatt line are very much in line with my own observations with the 2 I have been able to try in my system to date (F1 & F5).