I have a booster seat that goes over the headrest and in the back seat of our Jeep for our 11 month old Jack Russell puppy. It works great, keeps her safe and allows her to look out the window. I wanted to buy a second seat for our other car so I did all the research, read all the reviews and finally settled on this K & H Manufacturing booster seat and I am so glad I did! Our puppy is 11 months old and about 14 lbs and is pretty much full grown. I picked the small size and it has worked out well. She is also able to sit in the front seat without setting off the airbag, which is a huge plus, as I would rather have her close if my husband is not riding with her. I liked the idea of a booster sitting directly on the seat as opposed to hanging over the headrest. It just seems safer and better supported. I had taken her in my car a couple times and could tell she was a little nervous as she has always ridden in a car seat. This is very easy to install. You just slide the car seat belt in to the slot at the bottom of the seat and buckle it in like normal. The booster completely fills the car seat. It is very soft with a lot of cushion. There are 2 attachments to hook on to your dogs harness or collar or leash. I guess one is for a second dog but if you don't have a 2nd dog you can just tuck it under the cushion, which is very lush and soft and cushioned. I knew my pup loved it because about a minute after I put her in it, she layed down and went to sleep. I want my dog to be safe (1), feel safe and be comfortable. This meets all 2 needs. It looks nice too, if that is on your list. After I posted a picture of it on Facebook, a friend commented that she had been looking at the same one for a while and so she immediately ordered one after she saw how happy I was with mine. Big dogs can obviously brace themselves against turns and stops, etc, but small dogs cannot. This keeps them stable and safe. I hook mine to the back clip on her harness because I feel like that is the most safe but there are a lot of ways you can clip them in. The added bonus is that your smaller dog can now see out the window, which also makes them feel safer, protects against car sickness, etc. I am VERY happy with this booster seat - it meets my safety criteria but my dog's comfort. I have attached pictures. You can see that she has plenty of room to sit and turn and lay down. There is definitely room for a bigger dog than 14 lbs in there and if you read other reviews and look at the pictures and read the weight recommendations, you should be able to get a good idea of what size your dog needs. The pictures helped me a lot. Again, my puppy is 14 lbs and has plenty of room in the small. I believe manufacturer guidelines say a small is suitable for dogs up to 25 lbs if I am not mistaken. Great, great purchase. I am so happy with this.