OK I've got to fess up. I bought a Radwrench some time ago, but it was metal of some kind, not nylon! It's quite good at holding radiator valves & I do carry it around in my hand tools bag. I'm not on 'the tools' as much as I'd like & i'm very selective as to what I carry, so I'd give it a 8/10.
Have to agree that the Radwrench did look handy, and certainly the most promising thing in their range as it's cheap, simple and no doubt cheap to produce.
Mind you, I only do plumbing on a DIY basis, so perhaps the pros already have better ways of working on rad valves without scratching them.