RE: Flex Shafts???
U-joints are becoming a thing of the past---strictly an opinion. I believe flex cable gives you more adjustment. Not only that, you have the ability to custom size, fit it, and grease it easily. U joints were made for axles, and CV half shafts. Not a point of stress during a turn on a rc boat cranking out 15,000 rpms or better. Again, strictly an opinion