I have the Lost Ranger bag and the Air Core insulated mattress but I have never slept in it. My wife uses it all summer long. With this system I/she would highly recommend an insulated mattress.
When we camp together she sleeps comfortably inside her Big Agnes setup while I use a 40 degree synthetic bag on top of an uninsulated Air Core and rarely get inside the bag. Go figure. I do spend most nights chasing my mattress around the tent, she never does.

Our 5 year old mattress has failed. It developed multiple seepage type leaks all on one end. We returned it to Big Agnes and are awaiting their evaluation and decision.