Your neighbor's set up sounds similar to ours.........I would not spend the money on ceiling radiant heat again.

16ft ceilings.

Have a good friend who has a large body shop, swears by the radiant, and that is why I put it in--------difference is........and I wasn't smart enough to notice it at the front end.........his guys work in the open most of the time, rather than under, and the size fo the "blockage" is one auto every few feet, as compared to a tractor plus this plus that.  So, the radiant works really well for that kind of open area setup.

Had to put a fan in upper level to get lot of the ceiling heat down------that's not a big deal......probably would need something like that anyway to circulate the air that would gravitate towards the ceiling.

What we found is that seems when working under the equipment a lot, or at least the equipment blocks the "line of sight" of the radiant heat.........just doesn't do the job like circulated warm air would.  It's just fine when you crawl out.......but while under.....zip.........like walking from the sunlight into a shaded area when outside.

We are now expanding the shop..........this summer I hope to put down cement in that area, and circulating heated water within that.........and will used forced air of some kind for the above-floor heat.........no more radiant at the ceiling.

I would bet the portable radiant would be great........just a matter of nature of the shop activity.