My temperature sensor is usually called "hand".
I have an Alphacool Eisball reservoir on top of my computer, within arms reach. If/when I want to know the water temp I just grab the reservoir.
Since the pump is running at a constant speed and there are no fans blowing at the convector I have little reason to constantly monitor the water temperature.
I've been touting the benefit of using a fluid temp sensor since I did my first loop. For silent systems or any system that is cooling more than one component it's very important to know the fluid temp.
I don't really understand why it's not something that isn't included by default in a pump or common fitting like an elbow.
What you should really do if you want it to be silent is use a controller that can target the Delta-T of water temperature over ambient temperature, like an aquaero octo. This has the added benefit of not screwing up your fan profiles if your ambient temperature swings quite a bit, like mine does.