CRAB:
In the car analogy, due you want single or dual circuit brakes, can you accept the weight penalty for ABS, traction and stability control, airbags etc etc none of which are essential for driving but all make it safer if something bad happens.
Yup I think the answer there is you want a reliable single system, and you can use the weight saving (weight not so critical in a car) to run the ABS, traction control, airbags etc etc
There's a much better safety yeild available in helicopters from other things than duplication the relatively complex and low yeilding engine at such a high cost to payload effectiveness, especially daft to carry enough spare engine to mitigate engine failure risk during the 8 second window of transition, especially considering the risk of prolonging, in an upwards and backwards takeoff, the exposure to tailrotors and other risks (about 30 seconds of that exposure instead)
Anyhow some twin maths can just work, if the helicopter is big and the risk of landing is most likely to be fatal, like over jungle.