I've played with Airtabs on my Audi wagon. Did a few A-B-A test runs, didn't see any worthwhile improvement. I only had the mounted with blue painter's tape, stayed on but easy to remove. Ended up returning them.
For over a year I have been curious about AirTabs on the vans (Sprinter, PM, Transit, whatever). Figuring that being a larger and longer vehicle, the effect of AirTabs would be more noticeable. I've even come close to ordering another set for testing.
But then I saw an older Sprinter with them installed. It looked goofy. Downright oddball. Approaching ugly. Since I expect any mileage gain will be a small percentage, I decided that I'm not willing to give up the looks for a wee bit better mileage.
Now if you're doing 100k/yr on the road, maybe they'd work for you. I'd still look at doing some A-B-A testing to see if they're worth it. Go do some test runs on a flat road, no wind, preferably a few miles long. Tape on the AirTabs, do some more test runs in same conditions (same day, preferably). Then take the tabs off and test again, you should get the same numbers as the first test. Thus, A-B-A,.
Had them on a small cargo trailer that I sold when purchased my PM. Not sure they were really effective, but did a lot of dirt roads and the back of the trailer seemed to stay a lot cleaner then trailers I've had in the past without them. I'd agree with Z, they look goofy so I guess that means it would be okay on a PM. Seems a lot of folks think our vans look goofy anyways.
I used 32 air tabs, 11 on each side and 10 on roof. The body lines did not allow installation as far rearward as I would have liked and some places the sides were contoured to much for an air tab to lay flat. The roof is also ribbed, so we just put them on the ribs. I bought my air tabs at Volvo trucks of Denver and had them installed by Denver truck and trailer body shop. The air tabs were $ 2.75 each and the body shop charged 2 hours labor. I feel the body shop did a much better job of installation than I ever could.