I found two 5.56 Recons that I like, they are almost the same but have one difference. One has the VIS option (Vltor VIS 12" monolithic upper), the other one has the "Forged Vltor MUR upper receiver featuring an anti-rotation interface with the handguard". Both have the switchblock. Do I want the one WITH the VIS, or the one WITHOUT it? What's the real difference? They cost about the same from Noveske (a few bucks difference). Thanks in advance. Harry Wanna kill these ads? We can help!