I bought the Aer disc container about a month ago. I love how it foams skim milk. Interestingly, it hasn't worked on other types of milk I've experimented with except skim and whipping cream. I have added a little sugar to the skim milk and got a thick sweet foam I've used on top of hot drinks for fun. It does take some getting used to the settings. It doesn't work to foam milk if the setting is too high. 
I tried muddling a couple times. Will probably do more of that in the summer. The foam is what I bought it for. Wish there were more recipes available.