#1 is a cut-away of a typical floater frame. A cradled panel attached to a ledge. So you have the frame, the ledge, and the cradle all made of wood.
#2 is a typical conventional frame - one strip of wood with a notch cut to hold panel
#3 is a "non floating" float frame. The frame, with attached ledge. So you have the frame and ledge made of wood but NO cradle. A cradle goes completely around the perimeter of a panel - so it requires almost as much wood as the frame itself. This adds cost and weight.
The panel on the NF Float frame is attached with a silicone sealant. It comes in a tube like calking. I use the type used to seal aquariums. To remove slide a knife or razor-knife between panel and ledge.
This is the same way I attach panels to cradles. It gives an option of removing the cradle if you want to frame the painting in a conventional frame.