Nothing. It might take a little longer to break in. I didn't use it on my B17 and it worked just fine. I did use it on my Team Pro but this was because it is a thicker leather. Anyone think road bikes look stupid with a Brooks? I'm struggling with taking my Fizik Arione off and putting my Brooks Team Pro on... It's a '98 Eddy Merckx TiAX. Sorry to hijack your thread.....
Oh that's good to know! I'm a bit of a cheapskate, so maybe I'll just go without and live with the longer break in time.