I think not... as taste trumps any other data to a degree. I'm not going to say using one wouldn't be beneficial if you're looking for something accurate to .1 degree. BUT no machine I've used/read about is going to maintain the perfect temperature within that .1 degree, especially at the group. I bought a decent digital thermometer and use the styrofoam cup method... to me that's close/cheap enough as I don't think most people can detect the difference in taste down to 1 degree or less. Later!
It's funny because I was just looking up and down the shop to find my. Prior to PIDed my La Marzocco, I used it from time to time to check my temperature at the groups, now I don't use it as much. I am dusting it now because I am still adjusting my Mirage and I need to figure out what the temperature is.
I find them to be a very handy tool to have around. I owned one when I had a Vivaldi (53mm) but that got sold when I picked up the Speedster. I borrowed a 58mm Scace to set the brew boiler PID offset when I first got the machine but it would be nice to recheck a couple times a year. I'd consider properly setting the offset on any DB machine a must do & it would certainly be nice to pass on accurate temp recommendations to your customers if you are roasting for espresso.
I've put together a list of what I need to build my own 58mm Scace replica & will start on that once I clear a few other projects. The most expensive part would be a custom length Omega T type thermocouple which would run in the $50 range for the one I want to use.