Yes that is correct. Here is a link to a great pictorial installation guide for the mudflaps: Molded Splashguard Installation
I haven't seen any reduction. I have had better tanks than the best tank before I put them on and I have had worse but I see other reasons for that, heat, speed, load etc. Best tank pre-mudflaps was 4.2L/100km current tank heading toward 4.0L/100km.
A good friend of mine helped me install the mud guards on my 08 without removing the wheels, front or rear. He used an offset screwdriver and even installed an extra screw in each rear mud guard for good measure. If you have the right tools or the right friend, you should not have to remove the wheels.
