Those are Magsafes being sold by a third party (which is perfectly legal), not Magsafes made by a third party. There are no Magsafes made by anyone besides whichever company Apple has contracted them out to.
Not quite - those are replacement 3rd party adaptors (non-OEM). They are fitted with Apple-made Magsafe connectors but the bricks are usually made of nasty white plastic and are thicker than the originals...........
last I heard Apple was trying to stop the manufacture and sale of these things.