Is the sapphire crystal worth it over mineral glass?

Yes, if scratch resistance matters to you. Sapphire is far harder than mineral glass, so daily knocks against desks and doorframes are unlikely to mark it. It is the main feature that separates this watch from cheaper quartz models.

The 10 ATM rating means it is rated for swimming and showering, not for diving. Rinse it with fresh water after pool or sea use, and avoid pressing the crown underwater.

Does it need a battery change?

It runs on a quartz battery, so expect a replacement every few years depending on use. There is no automatic winding and no mechanical servicing schedule.

How does it compare with a Seiko 5?

The Seiko 5 is mechanical and appeals to buyers who want an automatic movement. This Citizen is quartz, so it is more accurate and needs less attention, and its sapphire crystal is tougher than the Seiko's mineral glass.

What is the 24-hour display for?

It shows time on a 24-hour scale, useful for reading a second time zone or telling day from night at a glance. It is a small sub-dial, not a full second-time-zone hand.