I wish I could give direct feedback on these compounds but I've experimented with a lot of different compounds and the predecessors to what your looking at (for whatever it's worth).
The ECF's we're supposed to dethrone the RS4 in the budget endurance market and from what I've seen seems to be accepted as a better RS4... similar wear rate, drivability, a hair faster, and a significant improvement in wet performance. However, it hasn't gained much popularity because of their price. The marginal improvements from RS4 to ECF's don't justify the huge price gap, which is why they haven't gained popularity IMO.
This is going to get a lot of hate, especially from the time attack folks who love the cheaty A052's, but I've never been impressed with anything made by Yokohama. The AD08R's IME were one of the worst tires I've ever run, the A052's were fast but poor feedback and wore faster than a hoosier R7 and any other super 200/100TW tire. IMO yoko can't make a tire that's fast, fun to drive, and can last long while the other half of the tire field figured it out over two years ago.
Have you looked into Falkens offerings? The RT615k is a pretty close rival to the RS4 for a budget fast and long lasting tire. The RT660 doesn't last very long, but about twice as long as an A052 and comparable in pace. V730's also bridge the gap between time attack and endurance tires and are cheap.
tl;dr: ECF won't be the wrong choice, stay away from Yoko IMO, and see if there's anyone else out there in your size.
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