I must be lucky I hardly ever break them and have done lots of them, I go around the window a few times with the one handled blade and the T-handle cable you pull on,
if you cut the tar a few times it seams to be less grabby, sometimes if its a little grabby after I cut a side and its loose I will slide a thin piece of a piant stick or whatever to hold most of the corner up and go to the other side and cut it again and slowly tip them forward away from the roof line.
they also make a neat electric tip one man cutter its slick lot less grunt involved when pulling it around,
