Normally after running on veg for a while you will find the vehicle is a little quieter, runs a little smoother and is generally better. Why? I dunno, its documented somewhere if you look though.
I'm using about 60% veg now sometimes more with no known problems.
Considering that most of my mileage is off road and in low box in the rough stuff, I'm pleased with the MPG which is about 28MPG (27.3) last check and varies little, maybe 1 MPG or less either way.
Price is going up all the time and is now only about 30p cheaper than fossil fuel. Much more and I don't think I'll bother making the effort for such a low saving.