www.MG42.us

Bought this one off of a French vendor whilst in Belgium, is this a legit one? It's having some issues not getting past the trigger group when I try to cock it, too.

The slab-sided charging handle didn't work well because it lacked mechanical-advantage leverage to overcome the grip of the rollers in the barrel extension. If you've ever "tested" a bolt by latching it into a barrel, you see how hard it is to remove.
Some photos of the French slab-sided charging handle. It's very nice. The one in your photo looks a little flabby in the tab that contacts the bolt, might need some fitting to clear the F/C group.
Nice score! Let me know if you ever tire if it....Phil

While I can't say whether your slab cocking handle is genuine or reproduction, there is a French guy who makes very nice reproductions of many things such as the slab handle, and doesn't identify them as such when he sells them. He's a regular seller on ebay, too.