Have been eyeing products like these for awhile and have not been satisfied with available options. Chose BCM’s and am glad I did. 
Cons: For my system, a $500 workhorse AR, the covers seemed to be almost too tight to snap into pos, had to use a small rubber mallet once they were started to get them to snap in. So be sure of your positions before using.  Not quite as wide as I thought, but its a minor issue that has no impact on performance. 
Pros: Once they are fitted in they are secured. 
Good grip potential
Cleans up the look of the rifle and coupled with the mod 0 fore grip makes a cheap system look top tier.