Use of sharp implements is encouraged, yes! I usually just take secateurs -- handily hook-y! -- to the rootball and rip at it vertically several places around.

Plants falling over with frost is not a problem here, but wind rock is a big one. I've seen shrubs that had gotten quite big, but were tipped over, and it turned out their roots were still in a 2L-pot-sized ball, swivelling in the earth like a socket joint with maybe one poor root actually attached and feeding the top!

Also when picking a plant at the garden centre it is -- so long as you don't drop it, and obviously also don't injure yourself -- allowed to tip a plant a little ways out of its pot to have a look at the roots.