I seriously would advise against it. If the first ball goes in, the second one probably would go in as well. There are a lot of anal toys that lack a good base to make them butt safe, and it is a shame really. I always advise against using toys anally unless they have a good sized flange base. A smooth ball shape is not going to stop a toy from getting sucked inside. I don't own a set of anal beads yet because of this...I just don't feel most of them are safe.
The material is another concern with the smart balls. The Elastomed is non porous, but not technically sterilizable. Fun Factory advises against boiling them even.
Bottom line is that these are intended and designed for vaginal use only.