Is the Coldpack 3 Thermo Mid WP actually waterproof?

Yes. The upper is built as a waterproof mid boot, so rain, slush and wet snow are kept out. Water can still enter over the collar in deep snow or puddles.

What does the Vibram Arctic Grip outsole do?

It is designed for traction on wet ice, the slick surface ordinary rubber lugs handle poorly. It is not a substitute for care on steep or polished ice.

Is it warm enough for freezing weather?

It is an insulated winter boot, so it handles typical cold winter days. In mild weather or heated indoors the insulation can feel too warm.

How does it compare with a tall pac boot?

It is lighter and easier to walk in, with ankle support from the mid collar. A tall pac boot offers more coverage in deep snow but more bulk.

Can I wear it for winter hiking?

Yes. The waterproof build, insulation and ice-focused outsole suit winter trails. For long approaches in mild conditions a lighter boot may be more comfortable.