Love the article HERE at Small Notebook
Why DO we use sippy cups? They get lost, are difficult to wash (plastic bits fly all over the dishwasher if they aren't corralled) Some are difficult to hold for a little one because the width is NOT child sized so they slip out of their hands.
I am a Montessorian. We teach that all practical life items be real but sized for a child. So a shot glass or plastic medicine cup is perfect to teach a child how to drink....before they give up the bottle so the transition is easier. They should be taught how to use it. Model how to drink out of the cup, then hold it for them as they grasp it, then let them try it themselves. Stay with them. Take the cup with you when you leave their side. If they ever toss the cup, the natural consequence would be taking it away from them until they learn to place it down.
So many children's products are designed to make things easier for us and not the child. Hmmm, something is backwards!