Yes the fin is pinned to the grip.
Yes, the Mission First Tactical Engage AR15 Featureless Grip will fit an AR9 as well as any AR15 pattern rifle that accepts standard AR15 style pistol grips.
No, this grip would not fit a SCAR 16S due to the high beaver tail and high blade/fin.
This grip will favor a right-handed shooter but can still be used left-handed as well.
When I wrote the question, it was submitted to an "expert" from the grip company. The answer was that the fin can be removed from the grip with the removal of two plastic pins. Upon receiving my order, I can see the pins that hold the fin to the grip, but have not tried to remove them. The grip comes with 4 extra plastic pins should one break.
Yes, this grip will not interfere with the safety.
Although I am not left handed, I held my rifle with the Mission First Tactical Engage AR15 Featureless Grip in a left handed position, and the position of my palm on the fin actually felt more comfortable than with a right handed hold. The reason for this might be that the fin is indented on the right which allows the palm to sit in a bit- not uncomfortable but different. The left site of the fin is flat, and seems to position my grip a little more naturally.
Yes, it does.