Hi Gaz - I considered one of these recently; having fallen too often into the category of buy something expensive/use it sporadically/sell it on I decided to break tradition and opted for a pistol grip which screws into the tripod foot of my lens (a Nikon 300mm f/2.8 in this case). Although I'd never trust the grip as a 'single point of holding the whole set-up' at any point, the comfort in your hand at what should be the lens' centre of gravity coupled with holding the camera body in the usual way makes quite a nice set up for me, which is usually 'in anger' against birds in flight. Anyway, maybe worth a punt for around £12 versus the cost of a Bushhawk!
Cheers
Mike