They are, by their very nature, a compromise tyre and need to be judged as such.
They will not perform as well as winter tyres in very snowy conditions and nor will they perform as well as summer tyres in the extreme heat of the summer.
They will perform better than summer tyres in wintery conditions and they will also perform better than winter tyres in the summer.
IMHO I would imagine that the all-weather tyres would wear quicker than summer tyres in hot conditions though. No proof of that, that I know of, at the moment though.