Is this the same size as a regular GA-2100?

No. The GMA-P2100M-4A uses a smaller, slimmer case aimed at narrower wrists. The layout and functions match the GA-2100, but it wears noticeably less bulky.

Is it good for swimming?

Yes. It is rated to 200 meters of water resistance, so swimming and showering are fine. It is not a dive computer and has no depth gauge.

Does it need charging or a battery change?

It runs on a standard button-cell battery, not solar. Casio rates the battery at roughly three years, after which a jeweler replaces it.

What functions does it have?

Analog-digital timekeeping, day and date, a 1/100-second stopwatch, countdown timer, alarms, world time and a hand-shift function. There is no Bluetooth or app pairing.

How does it compare with the full-size GA-2100?

Same octagonal look and toughness, smaller case and a softer pink-beige finish. Choose the GA-2100 if you want a bigger watch; choose this if the standard one feels too large.

Is the band comfortable for daily wear?

The resin band is light and flexible, and the smaller case reduces bulk on the wrist. Resin bands can feel warm in heat and take on scuffs with hard use.