I have the KS 27 Z with the 3D padded mesh back. I also got the internal pad because I needed a long internal pocket, and then I just took the pad out. It’s comfy when the pack is stuffed, and I think it is somewhat useful for the heat. I didn’t notice being uncomfortable ever with it on in the heat and humidity this summer.
His stuff is great. Looks good, very light, and it holds up well to a lot of abuse. I use mine everyday for work.
I wish the zippers went the other way on the belt pockets, that I had gone with 2L for the top pocket, and that one of the internal pockets was liquid proof, but other than that I have no complaints.
While his website is weird, I did much of the ordering via detailed email explaining what I wanted. He would then reply with what he thought was better and we went from there. Overall I thought ordering from him was a good experience.