Looks like one of those silly hex-key replacements for the takedown pin.
Look at the last picture, there appears to be a hex-shaped hollow in the top of the pin, and it isn't shaped like a factory pin.
What you're looking at is a gun from someone who couldn't figure out how to strip or assemble it to the basic cleaning level, and installed an un-needed fastener in place of the factory equipment.
I wouldn't take it unless it was cheap and came with the original mainspring housing attached to the original assembly pin.