1) This lens mount is for EF-S 18-55mm lens to EF mount modification. Please note that the EF-S mount lens is design for APS size camera, the image circle is smaller then 135mm full frame (24x36mm) camera. So we are not recommend to use the EF-S lens to shoot photos on a full frame camera, because it will result "dark corner", but it's good for shooting videos at 16:9 mode by using a full frame camera.
2) You can still use the modified EF mount lens on an APS size camera, nothing changed. You just change from a plastic mount to a metal mount, more durable.