Leaking thermostat housing, best gasket???

I really dont understand how the $100 one stops leaks. It still got to have a gasket in between then intake and thermostat (bottom section).

i wouldnt spend 100 bucks on any regular duty housing. it would seem to me that once you smash the O ring down, you wouldnt be able to re-use it. ive never used one . i would rather put that 100 towards something more useful. IMO. seems to me that if you still have to use a gasket it would be defeating the purpose.