Have a look at cleanshaving.co.uk I've just taken delivery of 4 of their cartridges and a free handle, their blades only fit their handle, cheaper than fusion blades, £2.50 postage but if you buy 16 cartridges you get free postage for £21.99, 1st order includes a free handle. Their handle is heavier than the gillette and in my opinion better. I won't be buying fusion blades again and I'm actually selling a gillette fusion flexball that arrived today without even opening it as I'm happy with the cleanshaving blades.
Suffice to say I have no connection to cleanshaving in any way. I found them whilst searching for cheapest fusion blades and based on their customer recommendations I took the plunge.