I have a Topeak Tourguide (the medium size) handlebar bag on order. It is 10.5 inches wide and 8.5 inches high.

I've never used a handlebar bag before (I would be using it for centuries, double centuries, etc, no real touring). Will this have a significant effect on aerodynamics? Will this potentially lower my speed or make riding more difficult? I generally like to keep a quick pace on centuries.

Also, will handling be (significantly) altered with an extra 2-3 pounds hanging off my drop bars?

I will probably only be storing some bars, gels, misc food, my cellphone, and a small camera, maybe a wind breaker. I use a bento box for nutrition right now (the kind that mounts to stem & frame), but it always sags, and isn't big enough for my cellphone.

The bag has gotten good reviews, do any BF members have any experience with it?