I have this one for my two, a 6 pounder and a 12 pounder, and it's plenty big. We drove to Texas and back and they did great. I don't use the tethers on the seat because it's so light weight though. Instead I tether them directly to the car's seat back. This helps keep the tethers from getting tangled around legs and tummies when the move around and it's a lot more secure attaching them to the seat. Plus the tethers on the seat are waaaaay too long to keep them in the seat where they belong.
[IMG]http://ecx.images-amazon.com/images/I/51G4wlq...