I used the BA Insulated Air Core on my recent trip.  It was awesome.  To the point where I want to convert to the BA System as soon as I have the cash.

Very warm.  On warm nights I used my sleeping bag unzipped as a blanket.

Very comfortable.  Great support when sleeping on my back.  My hips never touched cold ground when sleeping on my side.

I really like the logic behind the system.  Sleeping bags are useless for ground insulation since it's all compressed by my considerable weight.  I don't get any benefit from 1/3 of my sleeping bag, but I'm dealing with the weight & volume of that useless 1/3.  As a tosser&turner I do slide off my pad and my mummy-style bag gets twisted about.