I thought those cheap plastic guards were a waste of money until a client asked for a specific fade pattern.
A regular came in last month and showed me a picture from a magazine, wanting a very sharp, defined line in his fade. I usually just freehand everything, but I dug out an old set of plastic guards I bought for maybe $15 years ago and never used. I tried the half-guard to set the initial guideline, and it gave me a perfect, clean base to work from that I could never get as consistent by eye alone. It completely changed how I approach those super crisp skin fades now. Do any of you have a favorite guard or tool you were surprised by?