So what's the purpose/advantage of having a housing if we drill a hole in the thermostat anyways?

Whether you use the housing or just slip the prescribed thermostat in the hose and clamp it
into place, they both do the same job. So no real advantage performance wise.
With the housing I used, it uses a common thermostat that is in stock and available at any
auto parts store.

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U.S. Army Retired