Great for use as a spare.

This car seat is a lightweight seat that is ok for use for taller, older children. It is simple to use as you only need to place it in your car and your child simply sits on it and you place the adult lap and shoulder belt over your child.
I do not recommend this seat for smaller children or for any children on a daily basis because there is no side impact protection nor any extra back support for your child. Basically the only thing it does is position the seat belt in a safer position for children who have not reached the proper height for use of the adult belt. There are so many booster car seats on the market in various sizes that do have the side impact protection and back support along with multi positions to secure the adult shoulder belt. These seats are a bit more pricey but you can find ones that are still affordable for most. It is worth the extra money to offer the extra safety for you children. There are also many that allow the use of the 5 point harness for children of heavier weights, it used to be only to 40 pounds but manufactures have realized how much safer the 5 point harness is and brought their specs on the harness up to weights as high as 80 pounds.
So basically I would not advise this seat for daily use unless there is no other option. The price is reasonable and the seat seems to be built well for a simple booster.