The added accelleration and torque might be useful on Hills, on ramps, passing, etc. but its 50,000 lbs of weight I have to stop as well. Most of us don't put enough miles on our Coach to have the purchase price pay for itself over 3 years for the added mileage.
Lets say I run 5000 miles per year. At 5000 miles at 7 miles a gallon , which I average now, is about 714 gallons. At $3.30 per gal. = $2356.00
At 8 MPG / 5000 =625 gal. x $3.30 = $2062.50
The difference is only $294.00 per year.

The cost of the unit is approx. $2350.00 before tax.

So if the unit last more than 8 years it will pay for itself. It only has a 3 year warrenty.

For those who run 15000 to 20000 miles a year, and they are a small group, the savings would pay of in 3 to 4 years. As fuel prices increase, so would the incremental savings.
Also, how you drive your coach would also play a part. If you live in country with a lot of hills it might be more useful.

Anyway, I had a little too much time on my hands today so I thought I would go thru the numbers.