Is the MK6642 a good everyday watch?

Yes for desk and social wear. It is a quartz fashion watch, so it keeps time with little fuss, but it is not built for sports, swimming or heavy knocks.

How does it compare with Coach or Kate Spade watches?

They sit in the same designer fashion-watch class with quartz movements and similar build. Choose by the case shape and styling you prefer, not by specs, since the internals are comparable.

Does it need a battery change?

Yes. It runs on a quartz battery, which typically lasts a couple of years and is replaced at a jeweler or watch shop.

Can I wear it in water?

Treat it as splash-resistant at most. Michael Kors fashion watches are not meant for swimming, showering or diving unless the caseback states a water resistance rating.

What should I check before buying?

Confirm the case size and strap type suit your wrist, and check the stated water resistance on the caseback. Fashion watches are bought for looks, so try the size on if you can.