They are very earthy-attractive, strong, compact and incredibly versatile.  They also don't need coasters, which was wonderful for a large party I had.  I like them so much, I keep buying them.  This is my third (and probably last) set.  Out of 9 tables, several of them have slightly uneven areas between the slate pieces and things were so uneven that grout was used as filler in the corner of one table.  But for the price, I'm not complaining.  

Pros: attractive, strong, compact, incredibly versatile
Cons: slate may be set unevenly