I like that first one it gives the cadet a unique experience the others won't get often
The second one would give two cadets a chance at that unique experience.
For example Bob (Black) & Tom (Green) are the Riders who form Double.
Bob has a cadet named Tiffany, Bob (Black) & Tiffany (Green) can form Double.
Tom has a cadet named Britney, Tom (Green) & Britney (Black) can form Double.
Britney (Black) & Tiffany (Green) when they stop being cadets would form Double themselves.
That situation could have two Doubles at one time. Of course each Double would be different colors like Green & Black with Red & Blue or Green & Blue with Red & Black.
See what I did with the names Bob & Tom, Britney & Tiffany. Both male names are the same length & start with B & T. Both female names are the same length & start with B & T.