I've used both. Pro is indeed sturdier and has a better feel to it. It also looks nicer, if that's a concern. Both are accurate and I have not noticed any big difference in performance between them.
My x52 (not pro) I got used and eventually developed a problem that resulted in my dumping it for the Pro. Not sure if it was a manufacturing defect or if the first owner was just too rough on it. I hope the pro lasts longer.