Only works on posts with open topss, only works on frames with large cutouts in the B.B. shell, probably only really safe to use on steel frames and even then...
There are other, better methods which use intelligence (and/or chemistry) rather than brute force to overcome the seatpost-seattube bond.
Before I try caustic soda, has anyone tried this?: http://bikesfornoreason.blogspot.co.uk/2015/01/the-seatpost-from-hell-how-to-remove.html
This makes total sense to me, but seems to good to be true. Any thoughts?