I can't say enough good things about this product, and I never write online reviews. I bought the version with the RMR already installed on it. The instructions were simple and concise. Everything was labeled separately. It fit perfectly and like a glove. It is light but rock solid. Out of the box, it co-witnessed with the iron sights perfectly. Put 10 slugs through the M4 today, and it stayed rock solid and was dead on target. Thanks for making such an excellent product that more people need to know about!