interesting that you chose the small square pattern, some things I have lead me to believe it's the most comfortable option as it allows more even pressure and ventilation of your butt
with your other RDLs which stitching patterns do you have experience with ?
also intereresting you got the rain cover even with vinyl, does the stitching poke that many holes that moisture can become a problem?
I had half moons in leather on my RT, shown below. It was my first Russell. Both my pillion and I found it very slippery over time. My second Russell is on my Electra Glide, I elected to try vinyl and get the small squares. I think it looks as good as leather, and it is definitely grippier. This could be vinyl vs. leather, but I think the texture of the small squares helps. I too have heard folks mention that the small squares breath better, I don't know that I've noticed the difference.
The vinyl small square seats feel better to me, but there was also a process change at Russell between the time I got my original leather half moon version, and the vinyl square versions. They used to use foam from an outside vendor, now they make the foam themselves in house. It's suppose to be much more consistent. I did a ride in for the Harley seat and got to watch them doing the molding, it was pretty cool.
Russell recommends the rain cover when exposing seats to a lot of rain. I live in Oregon, I bought the covers for each of mine and have used the consistently. I haven't been in significant rain without the cover, so I'm not sure how things hold up.
With the cover in place, with pouring rain, when you are off the bike for a while you can just walk up to it, pinch the cover in the center, and shake it a few times. Your seat will be mostly dry and you can ride off comfortable.