The deadbolt is definitely a better lock than a standard doorknob lock. It is harder to break down or pry open the door with a deadbolt, since it is thicker and goes further into the frame. But really, if someone wants to get into your house, two locks instead of one is not going to stop them.

Is it OK to just have a deadbolt?

Yes, deadbolts are safe. But you probably actually wanted to know if they were secure. They’re about as secure as a cheap lock can be; they are mostly intended as a deterrent to someone casually wandering into your house, rather than to actually keep someone out, if they were determined to get in.

Is a deadbolt better than a regular lock?

Each lock type carries certain advantages; for example, a latchbolt will lock automatically, while most deadbolts require manual locking. On the other hand, deadbolts are widely considered to be stronger and harder to pick than latchbolts.