This mercury hour glass is charming.  Bought two, one for me and one for my daughter and her family.  Figured it could be used as a "time-out" tool for when the kids (or the parents) need some reflection time. And they can figure out 15, 30 min increments. 

Pros: Lovely sculpture and fun! It is not a toy - glass is delicate.  One arrived broken in transit and was immediately replaced by Wayfair.
Cons: None.