I thought I bought a Eotech 512 but there was a mix up on my part and it is the 511. However, I am not unhappy at all! It is super bright and clear. I am somewhat glad that it is the shorter 511 version because of my gorilla hands. If I used the larger 512 it would be a tighter fit for me to adjust or turnn/off the Eotech. This thing is pristine, came in the original box with instructions and everything. People with cheaper optics just don't understand!