Ive been using them for about three years now. Found them to be completely intuitive from the get go, and work as I thought they would compared to bar ends, which I wasnt keen on using.
I did however change the orientation position of the fd lever so that straight down its the mid ring, canted out to the left is the granny, and and canted out to the right is the big ring. This is a much more user friendly setup than the stock one, which they may have changed, I did write to them to tell them I thought their stock position wasnt great--but maybe thats because it works well for a double, I dont know.
It was a real bugger loosening the bolt to do this, i had to get a mechanic I trust do it as I was afraid to bread the damn thing. He very carefully heated the bolt without melting anything and all was well after.

All in all, I really like them. Setting up proper tension on the small bolt that determines shifting tension of the actual levers can be tricky. Well, not tricky, but start loose and gradually tighten, I over tightened it a bit and it was hard shifting. My rd doesnt have a barrel adjuster, so i had to install one in line up near the headtube. My first one was not good and kept slipping, and I didnt realize this, so messed around with actual shifter lever tension too much before realizing i had to change the barrel adjuster, and got a good inline one. Fine after that.

in photo, this is small ring position of fd. large ring would be opposite side.