I took Martian Coasters to the school group my kids go to. They have an open study hall. I had 3 kids playing Martian chess with me and about 8 others crowded around the table asking to play next. (which was over half the study hall)
So- it went over GREAT with the school age kids!
And the HOP that allows you to place a coaster anywhere else- you can place it so the 4 are no longer in a square- right? As long as it IS touching the group of coasters.