What's wrong with UN1 axles?

[law195]

I've been doing the research to build up a car and always come across the same thing. Use the adapters and Ford Granada CV joints with the Renault UN1/369 transaxle. What's wrong with using the renault CV joints? I see that the actual transaxle has splines off the box and only found one pic of the original renault CV 'cup style' CV joint. Is it a weak joint? or is the Ford version more.....(fill in the blank , cause I don't know). And wouldn't the axles and outer joints or hubs need to be adapted depending on the car (suspension, brakes, etc.) also. The main question is why is the Ford CV joints so popular. Thanks for any and all input.