Graham,
Got it in my 650GS.
Used to lose about 3psi if I didn't ride the bike for a week
(Gods way of telling me to ride it more

)
Now I lose no pressure at all and have great piece of mind.
There is something in the blurb about it keeping the tyre a bit cooler, but as I'm not on the ragged edge on a race track, I'm not concerned.
I've notice no difference whatsover in handling at any speed.
Read the blurn and you'll see they say it's okay for double the speed limit................
A chum was "so impressed, she bought a franchise"
For the medway area if anyone is interested.
I'm sure she'll do a GSClubUK deal if asked.
She's already had 2 punctures saved.
However - doesn't stop you checking your tyres regularly, like a good boy - but you knew that anyway
Cheers
Jon