Just got a [url="http://www.neckheavy.com/index.html"]"Heads Up"[/url] strap from the USA, but have since sold the bass I was going to use it for.
It really does work, and you can use the lead weights to get the balance just right, and because they are at the back of the bass you don't feel they add weight at all, just balance!
I don't want to make much of a loss on the strap, so asking for £45 (I paid £50) for it. I will cover the postage, which given the lead included will be substantial!
Cheers
Gareth