Yep, that one is pretty common where builders use slate as the sound board, with glass as the surface.
They open up the back wall to access the soundboard. It works well, but in my opinion is not a true double sided call. You have less than 1/2 the surface area to play on than you do on the other side. Mine have 2 full size playing surfaces, with a dedicated soundboard to each surface. Only draw back is its thickness. It has to be thicker to allow for the 2 soundboards.