What is your experience/opinion of spray on Polyurathane or Polycrylic protective paint?

I recently spray painted my wood end table (the frame... the top is gl inlay) and I thought it might hold up better with a poly coat. I bought a min wax water based polycrylic spray because the sale person said it would be low odor and non-yellowing. Well when I tried spraying one side it came out like little spots or bubbles everywhere instead of an even spray. Did I shake too much? It said 2 minutes. Did I get a bad can? Should I try a brush on finish or do you think it even needs a top coat? Im so over it at this point! I first tried this new rust-o-leum all-angle spray in espresso brown and the color came out much lighter.. a regular old milk chocolate brown which is not what I was going for, and the stupid nozzle broke not letting me stop the spray so it went everywhere! So I switched to Krylon satin black and it looks pretty nice so far... I just can't figure out a protective coat or if I even need one. (Where I can get a true dark espresso brown spray for future projects?)