Thanks everyone for your replies on the thread, I ended up getting the Ox earlier this week.
Really impressed by how well it works with the C+, all the clips online being with low-wattage Fenders and Plexis I wasn't sure what to expect. I'm going to leave a few impressions here in case anyone else finds it useful.
Boogie amp tones with the attenuator
I've dialled back the preamp gain a touch on both channels and rolled off a little bit of bass on the GEQ, everything else just got *more* in a very balanced and pleasant way all the way up the master (which I'm now running at 7).
With a touch of power amp distortion, the clean channel is an
insanely great pedal platform, it's suuu-per harmonically rich (Keeley TS808 and BB Preamp stacked is the best lead tone I've ever had).
The lead channel has a little extra wool on it that I need to work on dialling out, but overall it's incredibly full sounding, and like the clean channel it's hugely rich harmonically.
When pushing the power section to these levels the amp becomes highly interactive and incredibly sensitive to your playing dynamics. It's very addictive.
Even at living room volume, the sustain is outstanding.
This is a fantastic accessory for a Boogie amp, it's everything I already loved about my C+ but more, plus some new characteristics that were unavailable at lower volume settings.
The Ox itself
I found the speaker simulations to be really excellent; although I always prefer simplicity, the ability to select a couple of mics and adjust the room volume is critical (when you roll the room control back to get a dry signal you realise how dead it sounds without a little bit of this sauce).
I was put off the Boss Waza Tube thing instantly by how many features and controls it had, and it seems like the Ox strikes a nice balance between necessary features and simplicity.
The headphone output is fantastic, but sounds quite different to the line out to a DAW. This may be down to my setup, however. I am only running a single output, and there isn't a way to output in mono as far as I can tell.
Purely cosmetic, but I was surprised that the knobs are not perfectly aligned to their gauges on the front panel. A small thing but surprising given the price tag.
Another very minor criticism, but the built-in example rigs feel more like slightly gratuitous product demos than useable tones. I find this a bit disappointing, it makes an otherwise very classy product feel
slightly like a 90s Zoom multi-FX. This may say more about my early guitar playing experience than the Ox
At home, I'm only really able to run the speaker level on zero or one. There is a massive (>100%) jump in volume between 1 and 2. I am running an high powered 85W-rated amp at a pretty decent clip so this is likely less pronounced with a smaller amplifier.
I'm very impressed by the Ox. I haven't tried any of the others mentioned in this thread and elsewhere on the Internet, but based on my initial impressions it's brought a tremendous amount to my rig and I would highly recommend it to others.