correct. what it means in terms of performance is that you get a comfy ride on the street and better performance on curves.
downside is that you get too much bodyroll on low speed corners as the weight is tossed around. Suspension is also not as predictable as linear springs. They're essentially good for someone who wants to lower the car and retain ride quality to be decent.
That, and think about progressive geometry changing as you fill up your gas tank, or add a passenger.
If you're swapping out springs, there's no need to section strut housings. the strut housings are sectioned if you're lowering your car more than 2", and have to use shorter struts (not for 240/280z!) to fit the profile and retain the correct suspension travel without bottoming out.
Honestly, I think you're better off with just 4 linear tokico or eibach springs that fit stock