First I'll say clearly that I haven't got one of these or used one (did have something similar for a Stubai pole many years ago though). But I've spoken about them with ski-tourers/shop owners I trust in Aviemore and Braemar, and I reckon for ski tourers they have some merit - you have to stick with your poles until the ground becomes such that you remove your skis too, and if you've ever taken a slip with skis on a steep slope and attempted to brake with the pole-tip, then this is going to be a hell of a lot better.
For walking I'm a bit less convinced. In 'true' winter conditions I wouldn't see it as a substitute for a proper ice axe and, even if using poles, I'd have to say stash them and get the axe out before you reach the point you might need it. Then again, for those days when you 'um' and 'ah' about whether to carry the axe, or if (as I suspect a lot of us sometimes do) you get lazy about swapping from poles to axe to poles strictly as often as you might, then I think it would enable self-arrest in many circumstances and therefore isn't a bad thing. (Against that, the likely length you'll have the pole set at isn't going to be the best to facilitate self arrest.)
