The top is standard. The button at the bottom for catching the bolt is roughly 3x the size of the mil-spec part.
No, this only includes the bolt catch itself.
POF only provides that this is made of steel, they do not provide the exact alloy steel this is made of.
What? How would you use TWO levers in the SAME place?! To answer your illogical question, “no”. Buy one of the other! This is the best choice hands down. Takes up way Jess space and will fit most all uppers and lowers since this lever unlike the bad lever is built to have a little clearance so with most all uppers and lowers it’ll clear since it’s designed to. Just by looking at a picture you can’t see this so looks like it wouldn’t fit a gun with the OEM style bolt catch notch that some uppers have but will in most cases.
POF only provides that this is made of steel, they do not provide the exact alloy steel this is made of.
It's likely an internal casting mark to simply be a marking of the manufacturing run the part was made in. It has no significance on the sizing or fitment to the end user.