Yeah, the prescription side of their business is trickier. I have two pairs of Costa perscription sunglasses. They work well and I like them, but the coating has gone bad on both sets, one of them twice. First time, I thought it was a fluke, and it was still under the 2 year warranty, so they replaced the lenses. I was careful from then on out to only use good, name brand cleaning products with them (Zeiss and Bausch/Lomb). They were both bad again last fall. One pair was over the 2 year time, the other was not. No issue on the newer pair, but it was a fight on the older pair. My optometrist went to bat for me, and it ended up working out. But I'm a bit leary of Costa's CS. I know I'm most likely screwed going forward if/when the issue comes up again.
I only clean them with water and dawn dish soap now, per the optomotrist's suggestion. And I've found out that a lot of Costa perscription glass owners end up doing the same thing. They really need to figure out how to make coatings that last on those. So bottom line, I HIGHLY suggest you use someone else's glasses if you're going to a perscription set made. I have a WileyX pair that pre-dates either of my Costa's, and they're still going strong.