You see the reason for the price difference when you take it apart. They are not direct clones. I would not suggest putting the internals inside a real Glock mag. One way to upgrade them is to change the mag spring; $7 KCI mag with a $3 Wolf spring is still $$ less than a Glock mag, but close in function.
They do work well enough, but the lesser spring wears out faster.
They usually are not FML, thus not "drop free" mags.