In reply to robgixer:
They will add bulk, which makes technical climbing a bit more awkward, they will affect the fit of your crampons, and they will get shredded if you do any amount of mixed climbing. They were really designed for very cold snow climbing and are rarely used for much else.
They obviously add a bit of warmth, but you can't just put them on over boots mid-climb, really you need to put them on when warm in the tent/hut for maximum benefit (otherwise, if you do it later, your feet are trying to warm up already cold boot outers, inside the overboots). Putting them on early, in the Alps, would increase the chance of shredding them on approaches etc. and they may not fit in your ski bindings.
Too much faff, not enough benefit.
Maybe get a pair of Baruntses, they go to 48.