None of those are too good. For the most part, they're just keeping the honest people honest. Someone could get through one of those in a matter of seconds. People use them, but they really offer only minimal protection.
I don't know where you are going to school, but let me give you this advice. I am a freshman in college. I got my MacBok like two weeks before school started, and I was freaked out about people stealing it from me. I live in the dorms, where there are people around 24/7 and going into my first semester, I didn't really trust any of them. Now that the second semester's almost over, I would trust any of the guys that live up here with my life. I know them all, and I know that none of them would steal from me.(and if they did, it would be as a short-lived joke) We all have each other's backs, and if any one of us saw someone else's stuff getting ripped off, the robber would get his **butt** kicked. I never bought a laptop or external HDD lock, and I never needed one to begin with.