I don't have a 650b bike but I'm considering one. I think one of the attractions is the possibility of new life for nice older frames. For example, I have a very pretty Bridgestone RB2, nice purple color, looks new. I have newer steel bikes that are lighter and ride just as well or better. The RB2 will only take 28mm tires, max. It would be more useful to me if it did something my other bikes didn't, such as have the ability to use fat tires for gravel, rail trails, etc. With a 650b wheelset and long reach caliper brakes I could have a bike that is functionally different from my others. I don't think there are calipers that would make the reach to 26, so that's a plus for 650b over 26. Wish there were some less expensive 650b rims available.