I searched Google Shopping to find a reasonably-priced, effective car seat cover so that we would, hopefully, not have a repeat performance of the events of a few weeks ago, which involved rather difficult cleaning of the car seat following The Boy's loss of his breakfast on the way to an appointment at the outpatient center. I found the Messeez "One Size Fits All" cover and ended up purchasing it from Shopper's Choice, as you can see from the link.
I have not yet had to truly test the protection factor of the cover. However, it seems like it would do a pretty good job of that. It is made out of similar material to a windbreaker or the outer lining of a light jacket. It is machine washable or can simply be wiped off. Putting on/taking off the cover is very easy. The straps go through slots which are then velcroed shut. No need to thread anything through.
This car seat cover does not quite fit over The Boy's car seat. It hangs onto the edges. We have the Evenflo Triumph Advance in each of our cars. Granted, the EFTA is a pretty large car seat, but it doesn't look much bigger than the Britax Marathon or other such seats. The material is not stretchy, so it is difficult to get it to conform to the right shape. It also isn't soft or cushy, if you're into that sort of thing. The Boy still fell asleep in the car seat today and didn't have complaints.
At somewhere around $20, plus shipping, this is a pretty good buy. If you have multiple car seats, you can buy one cover for each, or you can buy multiple covers so that one can be washed while the other is in use. Many other covers sell for $75 or even $125.
Pros: waterproof, easy to use, inexpensive. Cons: doesn't fit as well over bigger seats, material not so soft.
It's worth the money that you pay for it. I wouldn't pay much more for this product. I am glad to have it, all things considered. Good thing to have, because most toddlers are messy.