Just got a used Fulldrive 2. I've been playing it with a variety of guitars from Strats to humbucking Ibanezes and here is what I've found:

From the moment I first turned it on I've liked it. It gave more body to the guitar and improved the overall touch of the instrument. I played for hours initially and kept doing so after everyone had gone to bed. I got no complaints just "nice" from the spousal/trekking partner (wife).

The unit is about the same size as the Radial Tonebone and is a light sky blue in color. The casing is heavy duty steel and there are 2 chrome foot buttons and 4 adjustment knobs.
From L to R: Volume - overall volume of the unit
Tone - subtle change in tone
Drive - that crunch that we buy overdrive pedals for
Boost - this is for the second foot switch. It brings the level
and gain up to wherever you set the knob

This is considered by some to be a boutique pedal. They aren't cheap, but already I feel it was worth it. Many artists I've seen recently were getting great tone and I would check out their stuff only to find one of these on the board or in their gear list. It's not a high gain distortion effect but an overdrive so it is not too crunchy or gritty. Just great drive.

It is somewhat similar in sound to the Bad Monkey, but the Fulldrive is better in the fact that the drive is much smoother. On the Monkey you can kind of hear the squareness of the wave, but with the Fulldrive those edges are rounded off and much more pleasant to the ear. The Monkey also has a bit of a mid hump that the Fulldrive doesn't have. With the Fulldrive you hear more body when you turn it on and your guitar doesn't appear to get colored at all. Just better.

The volume knob on mine allows you to pull it up and disengage the compressor. Whoa nelly! Volume up the wazoo. The compressor effect is subtle and not that noticeable in the first place, but with the circuit disengaged you get balls to the walls volume. It's hotter than anything I've ever tried for just sheer output volume, and...there is still the Boost button for more whompin'.

The Tone is a single knob that basically adds some highs or rolls them off I think. That is the way it sounds to me. The sound out of the unit has a bit of sparkle to it without a trace of harshness. Now the cool part...when you roll off your guitar volume it retains some of that sparkle. Sort of like when you put a capacitor in your guitar's volume circuit. It doesn't get brittle it just stays clear.

The Drive doesn't get buzzy when maxed it just sounds more warmly overdriven tubelike with grit.

The Boost when engaged gives a smoother singing lead tone without the square wave buzz. The volume increase is noticeable but not so dramatically different that your band mates or sound man will give you grief over it.

I'm thrilled that I discovered this pedal, and all the artists using it that may not so openly admit to using one for fear of the rest of us knowing their secret. It's a pedal, that because of the way I play, may just be left on all the time.