I went ahead and got myself one in the end. Lifes too short and all that....
I got it all set up (very quick and easy) and after a bit of fiddling about got a few chisels which could best be described as 'wide screwdrivers' or 'paint can opening devices' and happily discovered that within minutes they could be put back to use as bona-fide woodworking tools.
It's not immediately clear what angle settings will produce the desired bevel angle, and indeed using the recommended 25mm projection in the guide along with the 25 degree setting on the machine gets you to roughly 30 degrees.
I'm not overly bothered by this as it's clearly down to a bit of experimenting to get to the abgle I want. I actually found that I was getting a very good cutting edge at approx 35 degrees from a 180 grit belt straight off the machine with a merest flick over a strop to remove the tiniest of wires.
I put one of my ancient knackered Marples chisels that gets used on site through the whole range of grits, all the way up to the Hermes 2500 and then over to the leather coated chunk of Maple and the finish was truly remarkable. The whole process took less than 4 minutes, including getting some pretty bad dings out of the blade and correcting the angle from about 10 degrees out of square to bang on 90 degrees.
So although it's flippin expensive it does work well. It's well made and engineered to pretty good tolerances from what I can make out.