jky, that looks worth investigating, would be really easy to fit on to my trailer too, just take the current wooden runners off.
Do they make a big difference on yours?
Getting the boat on yesterday was easier than I expected (first time) somebody else backed the trailer into the water for me, nosed gently into place until it was resting on the trailer and then a few quick squirts of the throttle which shifted it about a foot each time until it bumped against the front of the trailer, mate drove vehicle out, job done. Getting it off was a lot harder, it seemed "stuck" to the trailer and lots of reverse thrust in shallow water just fills the boat up!
If I go for rollers I may just get keel rollers and lots of them, and leave the solid supports for the sides of the hull - with a few small rollers putting pressure on small areas of the hull it will get a tough time on the roads here which are very rough.
But I like the idea of those slides, it appeals to the lazy person in me who is looking for an easy solution not involving too much work
Edited to say: do you know if there is a UK supplier? getting stuff from the US to here is nigh on impossible. can't see anything on the website about UK agents.