What does prehung mean here?

The door comes already mounted in its frame with the pivot bearing hinge fitted. That saves hanging and aligning the slab yourself, but you still need a correctly sized rough opening.

Can I paint or stain it?

The hardboard face is made to be painted, and the listing calls the door customizable. Stain is a poor match for hardboard; plan on paint for the slab and trim.

Does the glass panel let sound through?

Yes. A glass insert passes more sound than a solid door, which matters for bedrooms and bathrooms. It is a better fit for hallways, closets and interior rooms where light matters more than privacy.

What size opening does it fit?

The listing does not state a width or height, so confirm the rough opening and door size with the store before ordering. Prehung units are sized by the frame, not just the slab.

Is this door worth it?

It is the only new option listed, so there is no cheaper new door to compare it with. A prehung glass door is reasonable value if you need light through the doorway; plain hardboard doors without glass usually cost less.

When should I buy it?

There is only one new-price listing, so there is no recent range to time a purchase against. Watch for door promotions at the store rather than expecting a competing store to undercut it.