I would also recommend the Grand for a first Reo. Sure, it's a bit bigger, but it gives you more options as far as where you can use it, due to a larger bottle and battery. With me, it lasts me the entire work day, whereas my mini (not 2.1, the little one) requires battery changes, and by the end of work day, bottle changes.
Both are very good to have, but if I were limited to just one, it would definitely be the Grand.