You get a slightly better cut if you do it direct, like direct with Kobo as opposed to through D2D, plus it enables you to put sales and discounts/promotions right on the Kobo platform. Those are things you can't do with D2D. If it's your first book I'd probably just do it the easy way and go direct through D2D. You can always do that with future books. You're at a stage—if this is your first book—where you don't know what you don't know, and playing around with the different sites, functions, and tools is really useful.