We own a Dynamax super C and love it . We run a 350hp Cat with Allison 3000MH Trans. We get great milage and power. You do get what you pay for so what ever you do test drive and ask questions of owners who own rigs like the one you are looking at. Iv owned Ford diesels and didn't have much luck with them . I always say the the bast truck is the one that doesn't cost you any money after you buy it. If you plan on doing any work on your motor make sure you check to see if you can get to it . I didn't like the idea of removing the bed to get to my motor to check for leaks or to clean it thats one reason we didn't buy a pusher.
We average about 10 to 12 mpg depending on how I push it. We came across the US and averaged 10 mpg and that was through Yellowstone , Mount Rushmore etc.
One thing we noticed was how cool the Dynamax stays running down the road with only the dash AC on. We went to Florida with six in the coach and did not have to turn on the generator for added AC.
Our next big trip is Alaska for 3 months.