I own both and like 'em both. I can't ride anything other than a Brooks anymore.

The Pro is noticeably thicker leather and not-so-noticeably more narrow. I put the Pro on my fixie as the handlebars are lower than the saddle. The B-17 is on my regular road bike where the bars and the saddle are the same height. (Also have two bikes with Flyers.)

I used a small amount of gloveolium (baseball glove dressing) on the Pro to try to speed up the break-in. But it did not seem to have any affect other than darkening the leather a bit.