Been using one of these for a while now, and it's become something of an 'essential' piece of kit. It's a great practice amp (Line in for iPod or similar) and a headphone socket that will also drive two 8Ω speakers, and the lovely tubey warmth and grit that we've all come to expect from Dave's kit.
The headphone output is a little bit 'hissy' but not massively so, and to be honest, once you start playing it becomes unnoticeable.
Where it becomes indispensable (for me at least) is recording; I use the DI out to go straight into Protools and then use the 1/4" output to go through the FX rig and record both channels at once - makes for an easier mixdown as I can blend just the right amount of effects with a lovely crisp, edgy valve bass tone. Both outputs have their own volume controls, so it's easy to get the right balance of output to fussy pedals (like the OC2 or ZVex Wooly Mammoth) that don't like a hot input signal.
Absolutely love it, well done Dave.