As always, the best advice is to try the SP20 in your system before purchase. A typical ARC dealer will be happy to let you do that.
+1, I agree with @cleeds advice about trial, if possible.
Personally, I would have to hear it in my own system to believe it to be as good as some say. I have not had much luck with full function preamps.
I like the idea of saving money and space theoretically, but I have been disappointed in the internal phono stages of the few that I have tried (Cary, VAC, BAT to name a few).