Cruise controls don't always work the same way. Most maintain speed (usually measured by wheel RPM, not necessarily on a drive wheel), but a few old ones maintain engine RPM. Most assume the only actions they should take to maintain that speed are to apply the accelerator or not apply the accelerator; a very few will brake or even change gears. All are supposed to deactivate when you touch the brake pedal; sometimes this feature doesn't work, while a few extend it so that touching the accelerator, clutch, or gear selector will also turn the CC off.
I agree with you about not wanting to use CC most of the time, except when there is a too-low speed limit that I feel I must obey; then the CC is a great way to avoid accidentally going faster.