I run thermal clutches on all my stuff and always have. When cold, they are very loose and then when the hotter air hits the spring, they get tighter. Non thermals are just the same amount of friction all the time. I also replace them every 3 or 4 years as they tend to loosen up with use. Especially on the Hemis that turn more Rs than the wedges. And because I run a cut down truck fan with big blades, I run a heavy duty or severe duty clutch.

Here are a couple of links that explain the difference better.

www.haydenauto.com/en/technicians-resources/faq-fan-clutches

https://itstillruns.com/difference-thermal-vs-nonthermal-fan-clutches-12246205.html