Poly block for underfolder conversion

[Ravenslair]

Has anyone used one of the Poly stock blocks that Copes sells? They allow you to use an underfolding stock on a standard rear AK trunion? Just curious if they are worth it (i.e., no rattle, can still fold the rear stock with a 30 round magazine - while out of state). I would rather get an underfolding stock and one of those blocks than have to buy another rifle.

Thanks in advance.