This may be a little expensive but I replaced my standard GSO focuser with a Moonlite (
www.focuser.com ) and would never bother using another focuser (except maybe a Feathertouch)
The good things is that you can buy an installation kit whic includes spacers, curved adapters for for all the standard size tubes including 6" and it is all predrilled to fit most major brands including Skywatcher.
If you decide to upgrade you can simply put your old focuser back and buy another curved adapter to suit your new scope and the focuser moves with you.
The great thing about these focusers is that they are actually an investment in your scope, the one thing you spend more time doing ,apart from observing, with your scope is probably focusing , so you want the best and easiest to use focuser you can get!
I bought direct from Moonlite in the US and their customer service was superb.
Cheers
Malcolm
PS the single speed version is very good ( I have one on my 8") but if the budget allows, the dual speed is wonderful!