hey folks, i got the S9 today for my mini 6. working with Delta and Retroarch out of the box. the fit feels solid -- way better than the razer kishi i was using on my phone. as for the buttons and sticks, it feels about the same as 8bitdo gear i've used. the rubber part on the left that goes against the top of the ipad is sized to fit juuuuust between the volume and lock/power button, like millimeters clearance. i use a smart folio so would take it out of that to use this, but i might get a slim case so those buttons are depressed and the S9 is less likely to hit them. it has another inch or two of stretch so i don't think even a bulky case would be a problem.
HOWEVER don't consider this an endorsement, the thing is pretty damn expensive (i paid $65 on kickstarter, it's $70 and that's supposedly an early price before it goes to $99) and i totally expect bugs to come up. passthrough charging is working now but was a little weird initially. i might come back and edit this in a week or so after using it, but in the meantime if you guys have any questions or want pictures let me know. i'm gonna be playing some SNES/GBA games, which look so gorgeous on the mini's screen.