I've got the aluminium Leo's 'cause I'm a cheap bugger, and they sound AWESOME!
I think that people pass over poor-ole' aluminium (al-you-min-ee-um for the UK guys) all too quickly just because CF and Ti are exclusive or special in some way. CF does give the option of having something that isn't silver, but I'd go for anodised aluminium before CF any day, especially on a twin. Under heat and cyclic stress (big pressure waves from the v-twin exhaust), CF can crack or become otherwise less structurally sound.