Scotch-Brite pads are very flexible, they are also much easier to handle when scuffing up an irregular surface, compared to working with a stiff sheet of sandpaper.
The Grey Smirdex Scotch-Brite pads/rolls are not an alternative to sanding. Instead the pads are designed to put fine scratches in the primer or paint. Good intercoat adhesion prevents one layer of paint from peeling from another.
The Red Smirdex Scotch-Brite pads/rolls are very fine grade pad, a perfect solution whether you are finishing flat panels or contoured surfaces. Ideal for awkward areas, like door shuts or engine compartments. Easy to cut into desired lengths for hand sanding or use with orbital sanders.