Any non-OEM belt available at this time seems to perform poorly on the XB's.
I went through two OEM belts on my Uly, the original D and its replacement F belt. Each lasted approximately 20,000km. At a value of $185, the OEMs cost about $0.00925/km.
I tried a Goodyear Falcon late last fall/early this spring. It lasted less than 4000km. At a value of $125, the Falcon cost about $0.03125/km.
Per kilometre, the Falcon belt cost me 3.38 times as much as OEM.
Plenty of discussion on BadWeb: https://www.google.com/search?as_q=G...ts=&gws_rd=ssl