Of course they can get root bound, idk where these guys heads are. As the roots hit the outside of the pot the get airpruned causing the root to split into multiple new roots, that's why these types of pot usually have much denser, fine root structures compared to a bucket grow. Any container can get rootbound if the plant is allowed to grow to big/long. I don't think you'll have an issue in flower, many people run complete cycles in pots that size,might just need to keep up on watering, if there is a large root mass it will drink and dry up quickly.