Our kids get limited if their only exposure is to the school's standard curriculum. I'd think making sure that topic coverage and range is complete makes sense (SAT does have some elementary geometry questions, too.)

Practice tests also make sense to me, particularly if he finds them fun. Helps to reduce some standard errors. Yesterday, in exploring apps with my DS who has a current obsession of finding the perfect math app on the iPad, I tried an SAT prep quiz. It had some area of triangles stuff. And I missed a question about the height of a ball after 4 bounces by forgetting to subtract the initial case in the calculation.