Don't take price as any indication of quality.
Cones measure heat work. Temp/time. You needn't be concerned with them if you aren't potting. A Potter who makes you think you do is bullshitting you.
A vitreous (from the Latin glasslike) pot isn't necessarily Frost Proof.
A Frost Proof pot isn't necessarily Vitreous.
Any of these can be had at any temperature/cone.
Not all cone 10 pots are Vitreous or frost-proof.
The only pot that is Vitreous or Frost Proof is one that has been tested as such.
Crackle glaze is a flaw or a feature. Glaze is also frost-proof or not, completely independent from the clay. So a porous glaze on a Vitreous pot can destroy the pot if frozen. This isn't likely.
Round pots are inherently stronger in their one peice construction, made stronger by being round. (Porthole theory)
But not every round pot is stronger than a slab built pot.
Different clays have different strengths and weaknesses. Different firing schedules make a difference, these differences are rarely observable with a look, sometimes observable with touch, sound, and lick, and always only fully known (if they are any good) by the Potter.
The unobservable part is the crystals within, which form the bonds that actually give a piece strength or weakness.
These crystals are what make it possible for any pot to break seemingly randomly, though most occur with drastic quick temperature changes.
Firing Schedules control these crystals. So the best made round pot can be rendered useless, and the worst made slab pot can be made strong, with firing schedule alone. Verified by cones.
Sorce