Brilliant brakes....coupled with the right lever ( Sd7, fr5, xtr, ultimate etc..) and the right housing ( odyssey linear slic etc ) and good pads ( avid standard ) they can outperform or equal most set-ups.
I run an old style BB7 silver road caliper with mountain internals, on a 185mm roundagon rotor, SD7 lever and Odyssey linear slic cable. It outperforms all the Hope mono trials that I've used, and a fair few magura set-ups. I reckon I'd change to a vee if I had the mounts, due to the performance and the weight loss though . Its worth bearing in mind that all types of trials brakes, be it HS, vee or disc can work admirably when set-up well.
The Avid bb5's are another good choice, as are the Hayes mx2's as cable brakes go.