I ran a Brooks Swift on one of my two bikes for several years.
It got about 50% of my 5,000 miles/year.
The break-in period definitely exists.
My butt broke in nicely.
After several years I finally had to admit the Brooks still wasn't as comfortable on the really long rides as my trusty old 1990's Selle Italia Flite.
I went on to eBay and picked up another Flite, then eBay'd the Brooks.