In candy making, the difference of a few degrees is the difference between a sticky unpleasant hard candies, hard brittle ones and caramel.

I've used shitty thermometers trying to make candy. It sucks. If you want it to come out consistent, you need a good thermometer. One that lasts longer than a few months is always nice too. I dunno if a $150+ one is reasonable. But a quality thermometer helps for sure.