I have used both the clip-on and instant read thermometers when making candy, and while the clip-on stays in the pot the whole time, it can also get candy splashed up on the reading that can obscure the temperature. Plus when stirring, I often end up knocking into it. For those reasons, I prefer to use an instant read thermometer and take the temperature frequently--usually once every minute or so, and more frequently as it gets closer to the target temperature.