As a Barista express person going 54mm is a regret. 58 is more versatile and compatiable. But the recommendation was more for budget purchases. Breville also d

As a Barista express person going 54mm is a regret. 58 is more versatile and compatiable. But the recommendation was more for budget purchases. Breville also do a dual boiler with 58mm which is more expensive but if you live in Australia is amazingly good value (often $900AU which is about $600US). If you have more money still get a La Marzocco or whatever :-) My taste is to avoid fiddly things that need too much skill like heat exchangers etc.