+1 on the Kronos and Artemis. These are nice in that users don't need to lug around extra mags. Some big pockets or a simple belt pouch/bag should suffice (except for ball spammers who like to slamfire the Artemis...)
+1 for the Kronos, for it's cost it's probably my favorite from the Rival Series.
High schoolers shouldn't have trouble with any of the offerings. Jr. highers would probably be able to use them, but might need instruction in proper full operation (not short-cycling, loading procedure, etc.). Artemis is a solid choice and functionally similar to the titanium.
so you guys recommend the kronos and artemis over the helios, apollo, or atlas? any reason why?