Both Mojo and LilyGrace have the small one and we love them.
One side has the big treat and the other is the "puzzle" end where they have to get the treats out of. I think it depends on what size treats you put in that end...We use Yorkie Yummies in ours.
The big treat, I don't think the dogs can get that out...they sit there and lick and chew on it.....it lasts awhile, but of course, not everlasting
Course, I don't let my two have the treat ball for a long time though.