IDK about that, I´ve been using them for almost a year now and they still perform very well. In fact they are very hard to break. Maybe UV rays can do some damage but I don´t really leave my copter under the sun.
They are for 5mm shafts, I really don´t know the DJI motor shaf dia. Making them 6mm is pretty easy. and they do come with washers for smaller shafts too.