Hi Dave, avoid the eBay ones, I have one and trust me it won't hold the 900 very well - my sb-24 is reasonably big and heavy and I never had confidence it would stay in!
I have one - I'll try and dig it out if I've not chucked it so you can see what I mean..
I now have a manfrotto umbrella clamp:
http://www.morrisphoto.co.uk/ProductDetails~ProductID~6069.htmlPlus a flashgun screw to go in the top:
http://www.morrisphoto.co.uk/ProductDetails~ProductID~4413.htmlYou could also use a superclamp and the flashgun adaptor and clamp onto your lightstand:
http://www.morrisphoto.co.uk/ProductDetails~ProductID~4067.htmlIt will not surprise you to know I have that too
