The top one looks like plastic that came from a worn mold and was painted silver. The bottom one looks like crisply machined metal. I'd probably buy the bottom one.
Top one looks like it was finished in a vibratory tumbler to deburr the parts before it went for anoziding/finishing. Though the burr on the backshell wrench flat is a little more telling IMO. Very hard to tell indeed
As far as the ones BravoV posted is a lot more telling, though the first picture has nothing I can nitpick, the 2nd set of pictures is where the story starts.
1:The cuts on the cord grip (I think that is what that is) on the genuine one are either helical or at a slant angle (cant tell) but the round bottom of the cut means it was done with an endmill, on either a 4th axis machine or if its an angled slant, then a 3-axis with a suitably oriented indexer would work. The round bottom would help prevent cracks on that as it gets flexed. The clone part was done with a slitting saw, so only 3 passes were needed and a saw should be a good bit faster than such a small endmill. The corners are potential stress riser on something that flexes, but probably fine in the grand scheme of things given it probably only flexes a few times in its lifetime. Plus saw blades with rounded cut profiles are available if they cared to.
2: Keying notches on the cord grip. Square vs rounded, Probably saved a setup step by machining it with an endmill while the part was perpendicular for some other machining operation, rather than up-ending it to cut a square notch.
3: Keying cutout for the pin insert: Again with the round vs square. But since this is a hole though the clamshell, the one on the right, was just milled though to get a functional slot. The left was either broached out rectangular from a milled slot, punched, or EDMed (Lol probably not. $ $ $ )
All around nothing particularly egregious that makes you say "Well shit that's not gonna work"
However given that the 'normal' metal LEMO connectors are chrome/nickel plated brass or nickel plated 'brass/bronze' (per their catalog) I suspect the metallurgy will be a significant portion of the cost savings in the clone. Springy bits out of brass instead of a nice phosphor bronze, cheaper grade of brass for the body, etc.
I suspect you might not notice on something like a camera cable where its the connector isnt getting abused because its connected to a $ $ Pricy $ $ camera.