I have one. Bought it as a backup sight mounted on top of the front scope ring of my ar-10 and have since moved it to a 6.5" .357 Blackhawk where it is much better suited.
There is a rather small "sweet spot" in terms of eye relief. At anything close to receiver distance, the triangle reticle is much too small. It grows as you get further away and is just right at pistol distance. You might be able to mount it in a scout rifle configuration or on the gas block of an AR with a riser.
Though it is not as noticeable at pistol distances (both eye relief and shooting) the horizontal line and triangle that form the reticle are not at the absolute top of the block of fiber optic. As a result, there is a green strip above the reticle that partially obsures the target. Makes precision shooting 100+ yards very difficult. It's not quite as crisp as the image you've attached.
They say it's parallax free but altering cheek weld makes the triangle jump around.
I like it as a pistol sight. For a muzzleloader, I would stick with peep and globe with fiber optic.
