I bought the Large Solv-it car harness for my hound just before Christmas. My dog is not great in the car for more than 20 mins and I thought this would actually restrain him in his seat, but it doesn't. If your dog is happy to sit in the back, looking out the window or sleeping, this is probably great. My dog wants to sit with me up front and will do whatever it takes to get there, crying and barking all the way.
Since this attaches to the cross strap, he just pulled the seat belt and walked up the center console. I fixed it by attaching his leash, that has a traffic handle, to the harness, and then putting the seat buckle through the traffic handle and snapping it in. That way he was secured much more firmly to a smaller area and couldn't reach the front seat. I need a harness that actually holds him in place! Plus, the large harness was a bit too big for a 40-ish lb beagle/hound mix, a medium would have been a better fit.
It's heavy duty construction, nonetheless, solid straps and connections, very thick padding on the chest piece.