Planetbox Shuttle or straight to Rover?

With the PlanetBox sale happening and LO starting preschool in the fall (she will be two in October), I'd like to figure out which size to buy. Is it worth it to start with the smallest Shuttle size, and transition to Rover in ~kindergarten several years from now? Or does it make sense to go straight to the Rover? My concern is if the Rover is really heavy and unnecessarily big, it could make self-serving lunch harder for a two-year-old.