I would highly recommend this product, the pups are safe in the back seats and would recommend to anyone with precious cargo.We purchased this for our 11 week old boxer puppy after trying/disliking a few different car harnesses and car seat straps (American Tourister, Top Paw) from local pet stores. Unlike the pet store options, this one actually fits her easily and securely! It is so adjustable in each direction, from neck to chest depth to strap length, that I fully expect it to fit her for months instead of just weeks. That is a HUGE bonus for a fast growing puppy that seems to outgrow items every 7 days. If you have a small/medium dog that will stay that same size, then I have no doubt that this will last you for years and years.The harness is so similar to her regular one that she doesn't freak out at all when we put it on. The seat belt strap clicks securely into the buckle instead of the awful design that just wraps around the car's belt ... this means you can *completely* control how much movement your dog has in your back seat instead of hoping that s/he won't pull hard enough to fall off the seat or reach/scratch the door. Best of all, the harness fits so well that you can just clip your leash to the sturdy metal ring when you get to your destination instead of having to change harnesses before you get out of the vehicle.In summary, this is a FANTASTIC harness at a bargain basement price. I also fully recommend the seller Grooming-Pet-Supplies - we ordered this with standard shipping on a Saturday and received it on that following Monday. I don't know how they got it to us that fast, but I'm so grateful. When our boxer outgrows the small/medium, we'll get the exact same item from Grooming-Pet-Supplies in the larger size. Do yourself and your pet a favor - order this harness!We initially purchased the top model available at Drs. Foster & Smith. That model was built to hold a semi in place, let alone a dog. Each buckle alone weighed almost as much as my dog. It was too big and would've never worked correctly (even though it was sold as being compatible with the weight & size of our dog). I did my research on Amazon and this model showed up. The shipping was terribly slow (one star dock), however one arrived we fitted it to our dog. The unit fits very, very well and I only seen one point where there could be a potential rubbing issue. Our dog didn't mind it at all and we took him to the vet a week later which is a 11 mile ride. There and back and his skin showed no signs of distress or rubbing and he never had an issue with it once. The bonus was that we could put the windows down more than usual without the fear of him jumping out. The leash part connected to our buckle easily (Mitsubishi Montero Sport). We're very happy with the product!You need to harness and seat belt in your dog, for the dog's safety and for the people. You don't want your dog as a projectile in a serious accident. We have a larger dog that we always harnessed and attached in with a similar design. We recently adopted a mini poodle mix and needed another for him. This is the perfect thing for keeping the little guy in place!The buckle end locks into a standard seat belt just fine. It wiggles a little as the buckle side of it is a little smaller than I would like, but it is in there solid.Our little max is a 15.5 and this S/M fits him just fine. Yes there was alot of adjusting to do and I had to cut some strap off because there ended up being alot of extra around the waste after sizing it on him. I could still adjust it smaller if I wanted to. I think the reviewer that said it didn't fit their small dog didn't know how to work the straps correctly. It definately adjusts as small as advertised.At $9.45 this is totally a bargain because you get both the harness and the belt attachment.I have a Pug mix with a pendency to want to be everywhere and anywhere when driving in the car. I was hesitant at first to buy this not completely getting in my mind how it would work but once I got it I was pleasantly surprised!! It's length gives him just enough room to move around it the backseat while keeping both of us safe!! The only reason I gave it 4 stars instead of five is I found the harness to be a little too tight around his neck but the buckle works just fine with our usual harness so we just use that, which is kind of more convenient anyway then I don't have to switch harnesses when we reach our destination.This is great how it keeps my dog buckled in while I drive. He likes to be on the floor during the ride which is not safe when not strapped in. All the other harnesses were used through the seat belt which would require him to stay on the seat. But since he likes the ground, I am able to adjust it to the length for him to be comfortable. Don't let the picture fool you. This harness is a small/ medium. I would have been better getting a small for under 10lbs. but, I was able to tighten the straps to fit. I will also have to use some sort of marking on the clips to know which end is up. Like with all harnesses on a small dog who is hyper, I often get it on backwards.Purchased for a friend--I already have a different, MUCH more expensive brand. However, I will probably be purchasing one of these for my dog. This harness is higher quality, the tether easier to use, and I LOVE that the tether is a little bit longer than the one I already own, but still keeps my dog safely "strapped in." Additionally, the length is adjustable, so you can decide what length you're most comfortable with.The one downside for me, as a Miniature Dachshund owner--the harness doesn't have the best fit for a Doxie's odd shaped body. However, it fit my friend's Cairn Terrier perfectly, and she's ended up using it as his primary harness much of the time.Think my dog is a bit like Hodeanie she's only a small dog but unless I do it very tight so it doesn't twist round it might be ok so I'll percivereTiny much too small for a normal size dog, would suit a puppy or "Toy" dogA good fit for my dog. No instructions with it, and it looks like I'd have to unfasten the seat belt buckle to make it fit properly. I clipped a carabiner under the buckle instead. We want to be able to use the harness in both of our vehicles.Much smaller than the picture appears, and the tether strap is shorter too. At full extension my small golden retriever can barely sit comfortably. Not recommended for anything larger than a small dog (Fox terrier sized).