That is correct. If you remember, or maybe have a friend or family member who does, about 20 years or so ago this was the preferred way to potty train over pull ups. It allows your child to actually feel what they have done, and encourages them to go to the potty so they don't have to feel that. In my personal opinion this is definitely the best way to potty train.
We actually have about 12 pairs of the Gerber training underwear, and we attempted potty training our almost 2 year old, but honestly he was having an accident every 45 minutes it seemed and with a 4 week old baby at home we were way in over our heads! These covers would be a game changer though!