We have both sizes but I actually prefer the small 3.5oz size for most things. I take the insert out for things like a smoothie or something thick and add it back in for keifer, yogurt, applesauce. These really help prevent messes if he is feeling like he wants to splash around in his food or dip his hands in it. He can feed himself without the mess. They are super easy to clean.
My 18 month old really likes using this as it gives him freedom to feed himself without me having to clean yogurt off of the walls and ceiling. It is easy to clean and I like that I can take the extra seal off for certain foods.