Has anyone bought any of these books? http://www.moems.org/Books.htm

It says grades 4-8. Since it's math contest, I would assume mainly mathy kids are participating so I wonder if it would be OK for an advanced rising 3rd grader or would you consider it mainly advanced 4th graders who would be participating and would therefore work for accelerated 3rd graders working 2-3yrs ahead. KWIM?