Just to chime in with my own experience. I have a cheap model that I picked up at Home Depot ages ago for $15 and it works like a charm on standard construction on all my internal walls. It has never given me a false/positive to date with plumbing or electrical boxes/cables ... whatever. But it does have problems with any walls braced against exterior stone walls. Defies logic and annoying, so I use the long skinny wood finish nail method in the middle of the wall and then measure 16" either way to find the studs. Of course a little patch & paint is needed afterwards but it's worth it instead of relying on molly bolts.
