I saw one of these little mixer gadgets at the thrift store last month for just over a dollar so I decided to buy it and see what it could do.
It turned out to be fantastic! I use it all the time and in fact I went back to the thrift store and got a second one that was smaller in diameter. That small one fits inside of a mug, great for making foamy hot chocolate or a latte. They have proved their value as a useful non electric mixer in my RV.
Small push down mixers are not a new gadget, they have been around since the early 1900s. But they have had a recent revival because of the popularity of lattes and other such drinks that use foamy milk. If you push rapidly they really do whip a lot of air into milk, smoothies, eggs and you can even make whipped cream with them. But they also work for mixing batter where you don't want a lot of froth, you are the speed control.
Easy to find on the internet...use these keywords hand push mixer wisk