What would you recommend for a free floating quad rail for a colt 6920? I have been looking at Troy industires, Daniel Defense and knights armament rails. Troy appear to be cheaper but they don't list the wait of their rails. Daniel Defense is pricey but some on ar15 forum think they are superior. Some Knights Armament rails state that an armorer is needed to install their products. I have also seen quad rails which have an elongated rail section which connects/floats over the upper receiver section. The colt 6920 already has a rail section over the upper receiver. Here are the questions: 1 What should I be looking for in these rails? 2 Are the any quality differences between the three brands? 3 Is one brands mean of attachment better than the others? 4 Do I really need an armorer to install the rail? If so Would that mean I would need the armorer to take the rail off when I want to clean the barrel exterior? 5 Should I buy a quad rail with the extended rail section to go above the upper receiver or not? Facts and opinions are appreciated, thank you.