Mechanical vs Electric fans question

I've run a thermostatically controlled puller electric fan in a 64 Barracuda, no mechanical fan. Worked fine and was great for quick warm ups in South Dakota winters. However you can not get more bulletproof than a mechanical fan. I've had electrics go out, Jeep Cherokee, and clutch fans fail also. Worse is a water pump. Not much stress on a water pump without the fan. What is a dangerous flex fan?