Great for potty training... but also handy for general diaper leaks, (infant poo especially ) eating in the car, and probably 10 other instances in which it has saved me from the tredious task of removing entire seat cover and having to wash it. Also great for on the go when accidents happen and you still have to get home!
We have exspensive car seats and repeated washings wear out the equally exspensive covers ( $80 to replace ) We are car seat nuts and don't generally use aftermarket stuff like this but I feel these are safe.
We have 3 kids in car seats and I have them in each...