David,
is this for clocks or watches?
If it is for clocks I would have no hesitation in suggesting the “Ollie Baker” mainspring winder, I dont think there is anything better or safer.
When I started I bought the “Joe Collins” Mainspring winder, it can do most things but it would not cope with a big fusee mainspring and quite often on chime barrels and carriage clock barrels the winding arbor goes through the barrel the opposite way, this make the Joe Collins winder impossible to use on these types of barrel. I dont know of any UK stockist of the Ollie Baker winder so you will have to buy it from the States but it would be worth every single penny.
Ollie Baker – http://www.youtube.com/watch?v=GCLYAasvt6M
Joe Collins – http://www.youtube.com/watch?v=6uOsZ_ZIvLc
Bergeon (Based on the old English Mainspring winders) – http://www.youtube.com/watch?v=_RtdfhKSxNc these are expensive 
If you are talking about watch mainspring winders then you would need to ask the watch guys on here.