I have the V1.2, Supposed different circuit. Wish I could be of some help, the version I have I use as a poor mans Echo Plex type boost. Works great at the front of my signal chain, also eliminates the need for a buffer.
I have one but it's not my go to pedal. I think it's very versatile with eq. I hate to sound like I'm reading from the Fulltone web page but it works great at the beginning of the chain to give your pedals some juice or at the end to compensate for signal loss. The eq is handy too. I bought mine to help balance some signal level issues I was having with guitars with different pickup output levels but never really used it for that. Never really tried it as a straight up boost. It is a good pedal, solid build.
Well I've now put this FB3 at the end of the pedal chain running on 18volts. Fantastic with the Jubilee, and its the extra ingredient I was looking for with my JTM. Its a keeper!!!
I have a couple of fulltone pedals with 18v options. Higher output, higher headroom. Makes a difference. Glad it works for you.
This is my second one, cos I’ve got the DejaVibe too. Yeah youre right about the headroom, its fine at 9v, but moves into outstandingly professional territory at 18v. Now I have the Xotic BB, HotCake, Pharoah Fuzz and FB3 on my board- I’m set for life with this overdrive pedals setup.