HF 21 gal. air compressor?

I think so, yes. Does it have a cast iron compressor? Please do yourself a favor and don't buy one with an aluminum compressor. Even if it's just a small one. You'll be wasting your money. But as far as size, I think it will handle spraying fine. It'll run a DA too, you'll just have to take breaks to let it catch up. Also, what "I" would do is look on your local CL and maybe find a compressor with a bad motor or pump or just a tank. You can plumb another tank in with the HF compressor and probably do really well. On the cheap too. I've done it before.
Back in Mo. my last compressor was a 80 gal twin used one, that was pretty wore out. But had a shop that did nothing but rebuild compressors. I had $200 rebuilt total, but it was still somewhat weak to me. I am an ahout out of Houston and I pretty much refuse to go there!
Back in the 70's my dad restored a 2 orse inline trailer, he did it with a 5 gal Sears compressor and a siphon gun. Top coat was F8 green metallic, he was a perfectionist it was perfect, but I hate to ay how long it took him, I did notice he had his red oxide primer pretty heavy.
I will check it out but I think that HF unit has a cast compressor.