It works well when I am in a rush. I did get some clumping one time with a REALLY cheap store brand of protein powder. That stuff would have clumped when mixed alone with water though, lol. I prefer the muscle milk pre-packaged ones that have around 30grams of protein plus the good carbs from the oats. I only use those when in a rush as well.
You could also blend the oats straight into a shake with a blender. AAP had a great shake recipe for that but I forgot where I wrote it down