I have used EoTechs, the 512 and the XPS, and Aimpoints, a CompM2, Comp CL3, T1, and PRO...the Aimpoints are a better sight in every single way.
I had wandering zero issues with the XPS. I had never contributed it to heat, but thinking back, maybe it was. It loved in a patrol car during the heat of the summer, so temps were likely well over 150 degrees at times. At the time, I chalked it up to it just being a POS.
