On my 5-speed, the cruise control won't engage (or "resume") unless I'm already over about 40 MPH, and in either 4th or 5th gear. That's the factory installed system, designed to work safely with a stick.
If I engage it in 4th, and shift from 4th to 5th, it will disengage as I pass through neutral. I'd have to re-engage it.
A poorly-installed aftermarket system might not work so well.