That's one thing I really missed about my Pfaff QE4 - no on/off button, although the new QE4.2 has one. I loved it for setting the speed for FMQ - one less thing to worry about, lol.
I used to use it all the time on my Janome, but now that I have an auto-pivot function (where the presser foot raises itself) and do a lot of machine appliqué I miss it less, as my hands are not reaching for the presser foot lever.