Cons : The glass pieces slide on the slick surface. Any bump or nudge of work surface scatters pieces. Also not good with area heating as the glue melts around the pieces and makes adding to the area impossible because it comes up the sides. Then you have a bubbly mess that hardens as soon as it cools.
Other Thoughts : I tried ironing the glass pieces to heat it up, but the glass starts to move as soon as it reaches temp.
It might be good for large pieces, but is definitely not for micro mosaic.