Are these stand alone kits? I notice they have 10 programable "secert missions". I would probably get one for each of my boys for Christmas. Their computer exceeds the minimum requirements. Will they need anything other lego items to play with these things? More importantly, are they fun for 9 & 10 yr olds? Is the Gigamesh G60, or the Shadowstrike S70 more fun? Would there battles be more interesting if both boys had the same model?