I bought a cold knife from MannLake when I first got started 4 years ago. Over the past two harvests, we extracted with a friend at a small-commercial honey house, where she used a hot plane device...
This year I extracted our own (with our new extractor, yay!), and used the cold knife.
Got it hot in a pan of hot water, wiped it dry with a quick swipe on a towel, and then drew it down across the and along the frame with a sawing motion.
I agree that it took a frame to get the angle right, and I did mess up one or two frames, when the comb came up off of the foundation.
But for $20 or $100...this one seemed to do me fine. Maybe when I grow over 20 hives, I'll go electric (like Dylan in '65) and it will save some time.
rickvv
Minnesota