the first one from cmmg will not work with a lefty upper. the second one looks to be, from the pic, identical to the cmmg it should work fine.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...