The Vizio uses an IPS panel produced by LG Display so will have similar picture quality characteristics to the LM4600 (good color and off angle viewing, but mediocre blacks and contrast). There isn't a lot of info on the VIzio, but there is on the LM4600 if you look around. Like the LG, the Vizio is not a true 120 hz panel but a 60 hz that uses backlight flickering to try to simulate 120 hz, the key line in the spec sheet being, "Effective refresh rate achieved by enhanced backlight scanning for stunning picture clarity." However, unlike the LM4600, the Vizio may actually have a control to turn it on or off. One thing different is that LG is edge lit vs the Vizio being direct lit. The LG will be a lot slimmer for wall mounting, but the direct lit of the Vizio should help somewhat with flashlighting and backlight bleed (a noted flaw of most edge lit LED sets to varying degrees), but does not guarantee that the screen will be free of clouding or uniformity issues. The LG is a 47" compared to the 42" of the Vizio.
I own an LM4600 but have not seen that Vizio so I can't give a direct comparison, but unless Vizio really screwed up the video processing, I'd venture to say that both these TVs will be in the same ballpark for picture. The big issue with Vizio for many is that they don't actually make TVs and that they usually can't be fixed, only replaced, when they break.