Again I had one go when I first got the car. I've changed it and so far its lasted 45'000 miles.
Doesn't seem to be failing anytime soon either.
So yes its expensive and overly complicated but they do generally last.
I imagine those that flush the system every year will probably help keep the thermostat in working order.
I usually flush mine least once a year and top up with the blue coolant or two year stuff. Not bothered with the 5 year coolant on the account I flush the coolant every now and then.
For about a tenner and 10 mins keeps the cooling system tip top.
I've also never had to replace a radiator or any other part of the system. (Other than the water pump when the routine cambelt change comes up).
I do like the idea of the Renault in line thermostat. I've kind of gone off the idea on the notion it fails shut.
Alfa 166 2.0 Twinnie - LPG and a few trick performance parts