Those tires have more grip than the Star Specs and don't overheat like the Star Specs can sometimes (I've experienced that in the summer some). I wanted to get a tire with max grip.
The Z1 Star Spec is a good "cool" temp tire, but on 215's, I still couldn't generate enough heat when it was cold and windy or rainy. So I really wasn't seeing the "cold grip" benefits nearly as much as advertised. Going to try the RS-3 and see how much this difference affects me.
I'm OK with street grip being lower if they are cool. I guess the wet handling might get hairy. I'd like to see just how hairy.
The tread wear on the star specs is poor too, I got about 2 seasons out of them. I expect faster wear with these. For the money, it's worth a try.
These will be a daily driving tire, but I will keep the Star Specs on OEM wheels around, for when it starts to get cold.