Linux Mint 18.3 Cinnamon 64-bit with all latest updates (6 april 2018): the applet doesn't show a tray icon in the panel. The panel just blinks when the applet is activated and no icon is shown! Please revise the applet, it is very useful because my notebook is very hot and noisy at 2.2Ghz and I want to reduce CPU freq sometimes to cool it. In case if the applet is abandoned and people look for another solution, I also found Indicator-Cpufreq in software manager, it works but it doesn't seem to have any settings.
Same problem in cinnamon 3.8.7 (18 July 2018).
The applet is also not working on Mint 18.3.
It works bad on Linux mint 18 and Cinnamon 3.2.