I haven't seen the White Riversides, but I did purchase a set of the "new formula" Universal white tires last year. All was good until the last month or so when they developed the infamous brown ring. Nothing will get it off. I only drove the car 10 miles and on concrete paved roads. Extremely disappointing experience.
I spoke with Lucas tires last week about their white tires, which includes the Riversides. They said that they haven't had any complaints, but that they they haven't sold many either.
At the end of the day, going with white tires is still a gamble. For me, I am going back to black and be done with it.