Is the Tissot Seastar 1000 Automatic good for actual diving?

Yes. It is rated to 300m (30 ATM) with a screw-down crown and caseback, which covers recreational diving. The unidirectional bezel tracks dive time.

How does it compare with the Seiko Prospex divers?

It offers a Swiss automatic movement and a much longer power reserve than most Seiko Prospex automatics. Seiko models often have better lume and more size options.

Does the 80-hour power reserve really work?

Yes. The Powermatic 80 movement runs up to about 80 hours when fully wound, so it keeps time through a weekend off the wrist. Accuracy is typical for the movement, within about -20 to +20 seconds a day.

Will the 43mm case fit a small wrist?

It wears large. A 43mm diameter with 12.7mm thickness and 21mm lugs suits wrists around 7 inches and up; smaller wrists may find it top-heavy.

The watch on its steel bracelet, a Tissot box and paperwork. It does not include a spare strap or strap tool.

Is it worth choosing over the quartz Seastar 1000?

The automatic adds a sweeping seconds hand, an 80-hour reserve and no battery changes. The quartz version is thinner, lighter and needs less servicing.