from what i've heard, most tactical rifle teachers, like dave harrington and whatnot, will advise against the L-grab. but, for me, it's natural with my right-handed shooting. left-handed, i shoot normal, and hold the handguards. the L-grab is hard to deal with when you've got extra weight, like a suppressor and a light, on the end of your rifle, but i'll only be dealing with a light and one rail section, so it works for me. the advantages i get out of it, like stability and having my hand right there on the magazine for mag changes, have no other conceivable downside. i believe that the reason teachers usually caution against it is because for a lot of people it restricts the ability to turn the upper body and engage targets without throwing things out of whack.
i've never had that problem. same as i've never had a problem with my face moving with a non-nose-to-charging-handle cheek weld when turning to address other targets on the sides. just do what works. most teachers will agree with that rule.