I currently have a Britax Frontier and Graco Nautilus and wanted a booster for our cruise and as an extra for occasional car pooling. I didn't want to deal with the fear of other people installing the seat incorrectly. Anyway, I just ordered the new 540 and found it at the lowest price at the following site. I'll let you know what I think about it. It's for my 6 year old 54 lbs.
http://shop.happymothers.com/shop/p...ontent=Car Booster Seat&utm_campaign=COY11027
http://shop.happymothers.com/shop/p...ontent=Car Booster Seat&utm_campaign=COY11027