Ribble Bike Builder WHEELSET HELP!!!

I am in the market for a new bike and will probably get a Ribble Sportive. The CSN carbon wheelset looks fantastic but from what i can tell not many people opt for these. Can someone tell me why this is please? Is there a better Wheelset available via Ribble for the same if not less money? The guy at Ribble said they are meant to be used in velodromes and that use outside could mean more drag especially in windy conditions.....

Also i will be buying this bike as an upgrade to my Specialized Allez Elite (2010). Any veiws on this? I want a carbon bike so thats whats driving this upgrade plus i have been offered a good price for the Allez. Thing is the Allez is comfortable as it has quite an upright riding position and i understaand the Ribble to have a similar ride and geometry. Any advise greatfullly recieved.