At that, the mileage won't be insufferable. I regularly pushed mine hard, and it still managed 21, 20 mpg on a really hard day. If I took it easy, I might get 22.5 out of it.
One thing to watch for: They really love to eat idler pulleys. I had it happen with mine quite a bit, seems about 80,000 miles is what you can expect between having to replace idler pulleys. When it breaks, it's an immediate shut down-- the serpentine belt runs everything, after all. That and the tensioner-- the spring will weaken and break-- . Pay attention to your "idiot lights", the first warning you get is that the Battery light will illuminate. That's you cue to shut the engine off and look, before you overheat or worse.
Other thing to keep an eye on: The electrical connections. Sure, everything under the nameplate is Mercedes, and you'd think something that expensive would be quality, but--- Mercedes put stuff in these vans that Ford or GM wouldn't dare allow. Some of it was really questionable.
Interior lights. I had to replace these, the originals didn't put out much light at all. I bought some lights from an RV shop near where I live, and the difference was remarkable.
Beyond that: The one I had rode pretty good, had good power and gave fair service. I bought it used, and if appearances are any indication it was used pretty hard.