To Mishimoto from CSF? Never heard that one before. I just replaced my Mishimoto thermostat(left) with 4k miles on it for my stock unit(right) with 6k on it after hearing too many horror stories about their craftsmanship, leaky radiators and failed thermostats. As you can see the seal is already busted on the Mishimoto thermostat. I had a friend who had a Mishimoto thermostat fail on his Subaru which resulted in a ruined bottom end. From what I understand they make a decent oil cooler!
I do have the CSF radiator though, so I guess I can be labeled as biased.