I used the $10 HF rechargeable spray bottle (http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=1102) to put a second coat of Rustoleum clean metal primer on my car's engine bay. The experience was pretty frustrating but the results look decent enough.

The bottle doesn't spray like a spraybomb (which seems like it atomizes the paint), so much, as it shoots lots of little globs of paint onto the surface. As I thinned the paint with around 25% of Penetrol, the paint on the surface of the car tended to level and now that it is somewhat dry there is a fairly uniform coat.

I had to continually pump up the bottle every two or three minutes and tried to get the pressure up to around 70 psi (50 is recommended on the bottle). The bottle would quit "spraying" when it got down to around 20 psi. Also, the instructions recommend filling the can 1/2 way but I had better luck spraying with it around 1/4 full.

After laboring through the engine bay, which was actually much easier than doing it with the foam brush, I went back to the trunk area. I was having trouble spraying any paint with the black nozzle (medium) so I switched to one of the green (fine) nozzles and with 70 psi the thing all of a sudden sprayed like glory, probably as good as an aerosol spraycan from the store. It held up like this long enough to do 1/3 of the trunk, then quit. I pumped it back up and got nothing. Then I switched nozzles again and nothing. I tried again and again (it wouldn't spray) and I guess the can was just finished. So I called it a night. I have another bottle I may try tomorrow or I may just do finish out the trunk with the brush and roller.

You may have better luck with a thinner mixture or by using mineral spirits to thin the paint. I did have some runs and tried to hit them with the foam brush to smooth them out, but there weren't that many.