although I agree that the B-side's does contradict what RB theme is, mature and cool, but i also really like Cheerful, fun, uplifting pop songs that is B-side. That feeling is MoMusu. MoMusu have that fun, bubblegum pop sound that i really like and enjoy. But i also enjoy their mature, kool sound as well. I love it that MoMusu/H!P can have different sounds, even if it doesn't sound original or authentic.
Tsunku mentions that RB is the start for a new MoMusu, and that's great as it may bring in and attract potential new fans or just music lovers. but imo, the b-side is something for the long-time fans, that are used to this style of music.