Hello, I currently own an old Gaggia Carezza and I am looking into getting a heat exchanger machine sometime soon. I am currently between an Expobar Office Lever and a Quickmill Anita however I have a question about heat exchangers in general. Is it possible to adjust the extraction temperature on these machines or is this something which only those with double boilers can do? If only double boilers can adjust the temperature then I might consider getting a Breville Dual Boiler, any thoughts? thanks!

Short answer: yes, HX can adjust the temp

Long answer: Managing the Brew Temperature of HX Espresso Machines

As an aside to those two, if you're the type of person that needs to have an exact number, even if it's not relevant, go with a PID and a double boiler. If you're happy with relative temperature and enjoying the results most of the time, go with a HX, it's really not that big of a deal to flush for X seconds then lock in and pull the shot.