havent a clue mate, (link to website earlier on in thread)but not much i shouldn't think, theyr'e a very simple device containing only a flap and a spring, and an adjusting thread.
I guess you specify the engine capacity in litres, and the maximum boost pressure, and engine max RPM and they supply them adjusted to suit. Or maybe you just keep tightening the spring until it doesn't trigger under normal conditions?
even if they're a few hundred quid its cheaper than the alternative
And on the subject of runaway turbo diesels i think all diesels should be intercooled too.....an intercooler(shrapnel arrestor
) is very effective at preventing engine damage if you get a catastrophic inlet compressor failure. I have replaced a few turbos and had to shake pieces of turbine out of intercoolers.