Great concept but failed in craftsmanship. Would be much better if made of aluminum. The plastic loses its ability to hold secure. Loosens up over time to the point it will unscrew without effort. Need to be readdressed and redesigned to better hold the lens to the camera.
Even if you never use fancy lenses, you will need this if you want a cap to protect your lens, and it does come with a lens cap. The only downside is that each time you take the cap off (by squeezing the sides), you risk losing it, as there's no tether attaching it to the adapter. It does seem rather expensive for its size and complexity, but oh, well. It really is necessary.