They are great for what they are. My first knob shells lasted me a good while on my OrbPoi, even though I've countlessly drop them on concrete/hard floors, and let kids play with them. My new ones that UltraPoi were quick to send me, will last just as long or even longer. They are easy to pop off, and easy to pop back in for when I need to charge the chips inside.
Thank you, UltraPoi!