I needed upgrade for my cheap Gaggia Pure and I needed to pick from this model and Gaggia Baby Class D. Sorry to say - I bought Twin. 99% of coffees in our house is a cappuccino and I thought additional dedicated thermo-unit would make our living easier and save us some "waiting for a steam" time. I was stupid...
The point is that though there is second "boiler" indeed it is too weak to make proper milk froth for two cappuccinos in 650 ml jug (one portion of milk in 350 ml jug is okay). It's power isn't enough to whirl the milk which is absolutely needed to "stretch" the milk. Of course, you can use so called "turbo-frother",the default panarello tip but you will get only that poor bubbly parody instead of pro-like froth.
With any other Gaggia, Baby Class e.g., you could do it with it's single boiler but having your top line Baby Twin you would not.