They're supposed to be really good and the Tarty boys seem to be really happy with them. I've been running DMR Moto RT's for years (2.2" front and 2.4" rear) and get on well with them. They don't have much (any?) puncture protection but I don't get much problems and still run relatively low pressures. I've heard fairly good things about Moto Diggers too. Your call really, all much of a muchness in terms of performance and weight I think.
It can only rust in the presence of water and air. If the spring was rusted it's been badly bled or has been sitting for ages unused in a partly filled state.
I've also been using pure (tap) water for about 7 years with no problems at all.
Why is the bridge/yoke type thing made in two halves and then welded together? Seems a bit random. Looks pretty sweet overall, no disc mount though = fail?
Yeah, seriously, don't mind me I'm just kinda anal about that sort of thing. As an aside, that post ^ is absolutely spot on and will get you validated far quicker .