The new backboxes are made of metal. Not sure if Metallica ever came with the metal ones or if they just used the wood ones with the speaker panel decal.

The hammer is from spinny-vinny. Not sure if he is still selling them or not.

Theirs nothing wrong with the metal. Just visually a little different.

Being a LE owner I think I'm obligated by some sort of contract to say the wood is far superior but in reality it comes down to personal preference. That shouldn't be a deal breaker either way. With Metallica the only thing to really watch for are:
- Does it have the updated hammer magnet board. If so, great, if not Stern will most likely update it for you. I see this has the updated Sparky board so I'm going to assume they also updated the hammer board to. Would be a reasonable question to ask though for a serious buyer.
- Was it during the run where their were some PF issues by the magnet. This game is prior to that PF run so no worries about that for this specific game.

Zero difference when buying a SAM game. When you go with a SPIKE game the lighting is different in the back panel. MET is a SAM game and whether it has a wood back or a metal one you still get the single light tube in it. With SPIKE the lights are on the board in the back panel.

The difference you will see will be in the camera settings or due to mods. Some people put tape on their light to reduce the backglass brightness. Some people also put active backglass lights in which will light the whole panel up more.