Anyone using these?

I see the point but wasn't sure if they could cause more long term damage if grit got stuck under them during a ride.

I wouldn't use the fork ones, they are tight on the stanchion and if something does get in there it'll be held firmly in place and cause damage – bring back fork boots I say, never had problems with those back in the day!

I use the shock one both on coil and air shocks without any problems – the coil spring holds it off the moving parts so no problem there, but I wouldn't use the one that goes on tight on the air shock, just a normal one and don't do it up tight on the slider, just have it there as a sort of protective sleeve to keep the muck off, never had any problems. But, I also take it off and clean regularly.

I'm sure you'll get lots of differing opinions, but that's what works for me.

That was what I was worried about. Especially due to the Fox warrenty.

I use one on my Fox Triad. Been on for over 2 years and no problems. I do take it off and clean under it fairly regularly. It's fairly tight on the piston shaft otherwise the crud would get in.

A solution looking for a problem.

Some bike designs cry out for just such a solution. They need taking off and washing every ride though, but you're washing your duds so not too onerous.