I had seen this for years and always thought abut getting one, after a brief test with a small generic pad/cover, I took the plunge and ordered one from Cool Covers.
It fits my bike seat perfectly, plenty of overlap and covers the entire seat including the sides.
Even though this is not quite the right time of year, you can feel the cool air under you and how it is keeping your bum cooler.
The first time I rode to work in heavy rain I didn’t give it much thought until I arrived and got off the bike to realise that I hadn’t been sitting in a puddle of cold water for the last 35 minutes.
Looking forward to the summer to see the cooling effects then.
I thoroughly recommend getting a Cool Cover, after 50 years riding it has been a bit of a revelation for me, cool bum and no puddles, plus I find it helps with comfort and location as I don’t slide under braking etc.