...The dot is the supposed to be 3 MOA. But the sight can be mounted on a rifle or pistol. Is it 3 MOA when sighted on a rifle (close to your eye) or 3 MOA with mounted on a pistol (arms length from your eye)...
I have an FFII (4MOA dot) that was on a pistol, now on a shotun. Your question is reasonable and got me curious, so I just tested it in the garage. Set the gun in a vise and fixed the dot on a spot about 6 feet away that matched the of size of the dot.
As I moved my eye away from the sight, it covered more of the target, i.e. the MOA of the dot grew as eye relief grew although at not at a rate enough to make a difference between pistol and rifle length. I was probably 8 ft away from it before I could definitely say it was bigger. I did notice that as the eye relief increased, so did parallax, which makes me think it would be better on a rifle or shotgun.
Could not test a longer target range as my garage is not 100 yards long.
I now disagree with their claim "it offers unlimited eye relief, parallax-free 1x magnification", but I still like it.
3MOA behind a deer's shoulder at 100 yards should be a dead deer.
When I had a cheap 3MOA red dot on my handi, I made targets that consisted of a 3"square with a very bold border. I would hold the dot centered in the square, shoot and adijust until the bullet was hitting in the very center of the 3" square.
Be aware that FF's have a low light cutoff. If you leave it on, but put the cover on it, the darkness of the cover, or the darkness in the gun case will turn it off. So will sunset. There is a lot of "shooting light" left when my FF turns off due to low light. A red dot with manual off and rheostat might be better for evening hunts.
Hope this helps.