LOVE the visp - I drink gramms (brand) protein powder every morning, and it's usually pretty tricky to really mix it together. the visp does it without any trouble! I also use it for creatine, electrolytes, you name it. LOVE!
I have both sizes. The small size is PERFECT to hold in the hand. I do wish it had more oz/was a bit taller/bigger (but not wider). The wide one is the perfect size, but it's harder to hold comfortably...