Never had or tried either but its been on my to do list for a while now to make one or both and compare.
Done some searching on the net and Dakine do one that looks ok (slider) Anyone use it and how effective is it?
Anyone compared a roller and slider? Which did you prefer?
Share your DIY's please even if they weren't a success and why the failed.
fail, attn. Mark 
I've been used the dakine roller bar for 15+ years, I can't believe more people don't use them. The single biggest benefit is that you never wear out your harness lines.
I used a sliding bar when I used to kite, they were much more comfortable on the lower back, I haven't used them windsurfing but I can see them being beneficial too.
i'd never tried a roller bar until a few years ago when the billabong outlet centre started selling off unsold dakine gear. i bought a couple of roller bars for $10 and have used one ever since, and I haven't broken a harness line in 3 years. i usually broke one every 6-8 months, along with a boom
the caveat with the dakine ones I have is that you need slightly longer lines to counter the diameter of the roller. instead of changing line length I just loosened off the harness. the harness line is a little more prone to unhooking when you don't expect it
if you are trying to learn some freestyle stuff, it's more likely to put holes in your sail if you fall on it. I've got all sorts of grooves and slices in my sails where the roller has run across them
