I just picked up a used Eotech 552 yesterday. Holo is pretty cool, but too unfamiliar for comparison. I find the housing ugly and clashing with the AR. Kind of like a digital dash in a classic car.Other optics are an Aimpoint Comp C3 and Ultradot 6. I like the U6 reticle choices and seems to acquire targets as quickly as the C3. Aimpoint has a crisper, more tunable point. No preference between the tubes, though the Aimpoint rep gets the nod if the SHTF.
Now if only BCG's come back in stock so I can finish my builds and actually use the things.