Good idea but poor quality. A lot of numbers can swap groups with each other and still work. For example: 2 and 10 could swap groups, and 90, 8 and 66 could all swap places with both 50 and 78. This often times makes it impossible to finish the grid without heavy guessing, even if you've somehow figured out the connection. You need to avoid that.

Yes, too many possible, equally valid, groupings, with no logic used to get the "right" ones. Shame.