It depends on the cost, My cherokee needed a new viscous coupling for the fan, but the replacment would have been around £150 + so I put electric fans on.
However the same was needed for my disco but a new coupling was only £50.
Electric fans are quieter until the're needed, but I found it sent vibrations through the body on my jeep. It wasn't a cheap one either. also it required fairly extensive modifcation to make it fit, but that was due to very limited space to fit a suitably powerful fan. (Big engine + tiny rad = huge fan)
As for claimed MPG savings I can only speak as I find, overall negligable.
Sorry to put a bit of a downer on them, but I think the manufacturer went to alot of trouble to select the right thing for the job, and if the cost of replacment is resonable it's just best to stick with that.
Cheers
Pete.