Yeah the Roadie's non adjustable but that's ok if you get the right size.
I think you need to consider what you really want the harness for. A harness that gives the best safety in the car isn't going to be the best harness to walk the dog on and vice versa.
You might need to get one of each
Hi out of those two I would go with PetBuckle if you want it for the car.
It probably says the Webmaster isn't recommended for car travel because maybe it's not safety tested for using it as a seat belt.