DP90 and the Krylon/Rustoleum Semi gloss are more grey than black. Compare a sample side by side and you'll see what I mean.
The Krylon/Rustoleum rattle can method is great if you are doing a weekend detail job, or will be completely redoing the engine bay at a later date, but want it to look nice now.
DP90 is a primer. Topcoat it with paint.
For a low cost professional job, you can use any brand of automotive Gloss Black enamel, just mix in a flattening agent, available from your auto paint store. I have used NAPA Martin Senour enamel with falttening agent and hardener, mixed to the "eggshell" recipe on the flattener label.
That being said, next engine compartment I do will be with a single stage urethane paint. Enamel is a bit delicate. The Ss urethane cures rock hard and will withstand much more abuse. Cost is about twice that of enamel.