Deep fryer / Candy thermometer for tea?

Sure. It’s a bit of overkill since you will never go above 212°F (100°C) with water, but as long as it is accurate it’s the same as any other thermometer (they are just rated to go north of 500°F). In a pinch I have used my digital candy thermometer to take water temps for tea.

I use an “instant read” dial type meat thermometer.
it was 7.00 at target. works great. the water does nit cool before you get a reading.

I would be concerned about precision if the difference between 175 deg and 200 deg is only a quarter inch or less.

I use a candy thermometer, which seems to be working fine for me. Just make sure you have the tip far enough underwater when you measure the temperature.