I just got a pair of the mittens this year. I can't say I've had any major falls, but the protection seems about as good as wrist guards. They are plenty comfortable and you forget about the guard part once you are wearing them.
I think they are only so/so in terms of warmth. It's tough to evaluate because the wrist guard part constantly touches your skin and for me that caused some moisture, which leads to cold.
My only real complaint is that the wrist strap is stupidly undersized. I bought the mediums (I have small hands and often wear small gloves) and I cannot come close to wrapping the strap around my wrist without cutting off circulation. I just ride with them hooked in the buckle, but not velcroed back on itself.
Durability seems fine so far, but I only have about ten days on them.