OK, I admit that this is a luxury appliance. You can definitely make milkshakes with a blender, but if you want thick, evenly blended milkshakes that won't clog your straw after 3 sips, the milkshake machine will not disappoint. I hunted for a sturdy machine at the typical consumer appliance vendors in the mid 1990's with no luck. Oh, there were milkshake machines, and some even looked like old time machines, but they just didn't seem to be durable or of good quality.
If you like the peace of mind that accompanies knowing you won't have to buy a particular type of appliance again, then you have to go commercial. Appliances are like furniture: adding the preface, "commercial", to an appliance is equivalent to adding the word, "ergonomic", to furniture—it will double or triple the price.
Our single milkshake Hamilton Beach mixer was a wedding gift from my sister-in-law. She bought it at a restaurant supply store. Hamilton Beach also makes a "retro" model, but it is all plastic and underpowered as evidenced by the many negative reviews I have seen. Stick with a regular blender of good quality over the cheaper milkshake mixers.