Thermostat or not

Most of the time running without a thermostat will actually run hotter for the reasons mentioned above but sometimes you get lucky and it works ok. Nevertheless aa thermostat will make the temp more stable.

In my opinion the thermostatic fan clutch type is the best. But of course it costs more. If I'm not mistaken (somebody correct me if I'm wrong) the thermostatically controlled viscous fan gets harder to turn as the engine gets hot but the non-thermostatic controlled viscous type pretty much remains the same force to turn it no matter what temp they are. That's the reason for the thermostat on some viscous fans, to make it engage better as it gets hot and have less drag on the engine when it's cold. At least that's my understanding of them.

I couldn't get the NAPA link to work so I can't comment on it. Summit and JEGS sells all types of replacement fan clutches. I bought one last year from Summit.