Great idea! I think this game has all kinds of benefits, and I really like the charity quilt aspect. They just sew them together with sashing, and they are nice quilts! But if people are playing by different rules it isn't fair.
I did make a key for mine by writing on the back seam allowance of any square that was ambiguous. It's not difficult. But, of course, if winning is the most important thing, then it serves you better not to create a key.