Is the Tissot Seastar 1000 Quartz good for swimming and diving?

Yes. It is rated to 300 m with a screw-down crown, which covers swimming, snorkeling and recreational diving. Have the gaskets checked at service intervals to keep the rating valid.

How does it compare with the automatic Seastar 1000 Powermatic?

The quartz version is thinner, lighter and more accurate day to day, and it needs only a battery change. The Powermatic 80 automatic costs more, has an 80-hour power reserve and appeals to mechanical-watch fans.

Does it have sapphire crystal?

No. It uses mineral glass, which resists knocks but scratches more easily than sapphire. Owners who are hard on watches often factor in a later crystal replacement.

What is the difference between the steel bracelet and silicone strap versions?

The watch head is the same; only the strap differs. The steel bracelet suits office and everyday wear, while the silicone strap is lighter and quicker to dry after swimming.

How often does the battery need changing?

Quartz batteries typically last two to three years. A jeweler or watchmaker can replace it and re-seal the case to protect the water resistance.

Is it too big for smaller wrists?

The case is on the large side for a dive watch, so it wears prominently on slim wrists. Try it on if you can, or check the lug-to-lug measurement against a watch you already own.