I wonder if this is as good / better than
http://www.aquapel.com/ which i've used a for a couple of years and not had a problem with. Typically picked it up off ebay for £7-10 a go.
Need to really clean the windscreen and any other windows you apply it to, then use the applicator and smear it all over a few times. Buff off and just keep buffing until it goes clear.
Then when it rains it's Star Trek time and warp factor 9!
It lasts and last compaired with Rain-X etc which also gum up wipers and overall are naff!