Magnetic “stud” finders find screws and nails, not studs. If the screws or nails are on the edge of the stud, you may be mounting objects dangerously to the edge of the stud or may miss the stud completely.
Zircon stud finders detect density changes behind the wall. Zircon centre finding models are even able to detect the left edge, centre, and right edge of the stud in just one pass.