We have a "big" household unit. It does a pretty good job on stuff inside the house, but expect to have to stop and refill it often. If you need to really clean under a hood that is an oily mess, you will be there all day. You get about a 3' square of decent clean per refill, but you will be redoing about the last 1/4 of it after a refill. The process of refilling takes about 10 minutes, so whatever you were cleaning gets cold and you pretty much have to warm up the edges again.
Under hood would be better with a pressure washer with a good degreasing soap down first. Gene