IMO…the biggest difference from a user perspective is the FX sit considerably lower than the eagle vision.
They also have a much cleaner design.
Eagle vision absolutely looks to be better built and have the option for mounting stuff
U can see them side by side in this post
https://www.airgunnation.com/topic/eagle-vision-vs-fx-adjustable-elevation-scope-mounts-comparison/
Maybe it's just my luck, but I have had a set of the FX rings crack along the base. I have heard of a few others on this forum with that same issue, yet have not heard about this issue using the Eagle Vision rings.
No slam, just a fact.
mike