Breakage is a possibility with almost any method of parting glued ferrites.Aye! Bewared, however, that said method not uncommonly leads to 'hot-spots' (with subsequent breakage or permanent shift of magnetic properties) and, in my experience, destructive arcing!
Inductive heating (via a loaded driver) -- or the solvent/heatgun technique described in the tutorial require more patience - howbeit said 'virtue' is, in this case, amply rewarded!
Neosid (where I once worked) the development technicians sometimes fired prototype ferrites in the microwave when it wasn't possible to disrupt the production conveyor through the kiln.
When ferrites get unintentionally magnetised, a microwave is a convenient way to raise them above their Curie point.