But, very robust, it is not really. After the first shell is after 3 days refracted at the upper left corner, my replacement envelope had held less than a week and is refracted at the exact same spot again. (Although I really Bypass very caring with my things.)
Of course, the shell still holds very well and thus also the lens. However, one should expect more for 30. After all, almost 60 marks for a piece of plastic.