I fitted one to my 200tdi 110 as I do a lot of motorway driving. It's quieter which was nice but... well painful up hills etc. I have recently tweaked the fuel pump and it's now a different vehicle. Lovely to drive, and I'm trying to sound proof it so the relaxed gearing is helpful.
If you do lots of 50mph plus driving and give it a little tune up I would definitely recommend, otherwise stick as you are.