Not as good, but considering its a few hundred bux vs. a thousand and extra weight, its "good enough" if you ask me. Just be mindful how you use it within its limits and you'll be fine. I use a +4 closeup on my 50/1.8 too. Gets me to about 1:2 mag roughly. Make sure you don't have anything in focus at the edges, since the CA and coma is bad there, but center 2/3rds of the frame is tack sharp.

I just use a cheap +4 singlet closeup, not funny macro converter etc, which is actually almost the same but sells for more and has more distortion typically.