Save your money and leave well alone or just remove the standard viscous TD5 fan. In the UK it is not needed even during the summer months unless you do a lot of heavy towing in low range. I have not had a fan fitted for more than 3 years and my engine runs no hotter than when it was fitted. I removed it because it was knackered and I did not want to spend mega bucks on a new one. I fitted my old air-con leccy fan on a manual switch but have never had to switch it on and I tow a double horsebox.
As for faster warm up I've not noticed any difference and my heater is no hotter.
As for fuel economy your defender has the aerodynamics of a brick so removing the fan will make no noticable difference even though it must remove some of the drag on the engine.