I agree with Tom, the K&N removes less dirt and junk from the incoming air which is not good for the engine. Stay with a factory air filter, it will trap more dirt then any other filter and as for improvement in fuel economy, there is little, somewhere around 1/4 MPG and that is not worth it.

 

I agree that the K&N is not the right filter for the Disco, if oiled improperly. I will also agree that the K&N style filters do little to nothing when put in the Discoverys. However I will say that i have personal experience with getting anywhere from 1-3 MPG increase using the filters. This has been in forced induction motors though, and diesels.
I am not going to touch the subject of if they filter better though...

 

My disco had a K&N in it when I bought it. There was no history of MAF sensor replacement, I've cleaned and re-oiled it and still no issues, with the MAF anyway. If you don't know how to oil it, don't get one. On this engine, I don't know if it makes any difference. It could be worse for all I know. Below is a link that I found interesting on the subject.

http://www.bobistheoilguy.com/airfilter/airtest1.htm

 

Ran a K&N for years, MAFS died. Some say coinccidence, I run paper now.