Is this jacket actually waterproof?

The outer layer is described as waterproof and wind-resistant against rain and snow. No waterproof rating or seam-sealing spec is given, so treat it as weatherproof for everyday snow and drizzle rather than sustained heavy rain.

How warm is it compared with a down jacket?

It uses thick padded insulation, which traps heat well for cold winter days. It is not described as real down, so it will likely be heavier and less packable than a comparable down parka.

What should I wear underneath?

A base layer and a light mid-layer are enough for most winter days given the thick insulation. The bulky fit leaves limited room for heavy sweaters.

Does it run true to size?

No sizing or fit guidance is provided. Check the measurements on the size you order and size up if you plan to layer thick clothing underneath.

Is it good for active outdoor use?

It is aimed at winter outings, outdoor activities and daily wear. The bulky puffer build is better for walking and standing around than for high-output sports.