Just put an older Fastfire on my Ruger MK III and I like it but at longer ranges, over say 20 yards, there seems to be some distortion. Is this normal?
Great little glass other than that.

I think many are that way, The high end more costly ones are better. I have stigmatism in my right eye and get a star burst which hinders longer range use. My Larue PredATar wears a Trijicon MRO and my grandkids see a sharp red dot, I don't. Is it possible you have stigmatism issues? If not then try looking through other red dots or similar products fr comparison.

It’s not the dot but the glass. Dot is pretty good, my vision is not great, but with other red dots I have they have no distortion

the range has nothing to do with the distortion....

The open sights like the FF seem to have more distortion than tube types. Shooting with both eyes open minimizes it for me. The fuzzy dot can be improved a bit by turning the brightness down, but that’s not always possible. Prism sights can be focused to your eye, making the reticle as sharp as a scope’s but may have some optical distortion too, and without unlimited ER, limit mounting options somewhat. I’m moving towards prisms because I really like the dead-sharp aiming point and battery-free functionality.

The FF3 is a better sight than the originals.

Correct, its just easier to see at distance that's all. As the targets get closer and the window gets smaller its harder to see but still there..

I think this is the 1st gen FF, need to look through a FF3 and see what the diff is.

The FF3 has manual brightness settings as well as the auto. My impression is that its auto works maybe a bit better than the original, but it could just be the difference in dot size, or my imagination. The easy access battery compartment is definitely real.