I have yet to own a single espresso machine with the ability to control brew temperatures. For once, I'd like to have that option. I would like to know that what I'm producing from my espresso machine's boiler to my demitasse is exactly what my bean roaster intended (the beans in my hopper would like to swim in waters of about 201 degrees). Rather than making an educated guess that my brew temps are at 203 degrees Fahrenheit after my hx flush routine, I'd like a little digital clock-looking display to tell me my status.
I've thought about an Eric's thermometer, but it wouldn't fit on my machine (although it is an E61). I've thought about a PID, but I'd still have to wait hours for temperatures to stablilize due to the thermodynamics of an HX. A double boiler machine is a pipe dream for the time being, given the hierarchy of my finances. Doh well... If you're an espresso fan, this is your life... I'm sure that in two or three years, I'll be yearning for the pressure profiling talents of a Synesso.