Practicing oral sex on realistic dildos is just as effective as having penetrative sex with the dildo. You can do both and enjoy them equally well. Most people do both. But you may enjoy one more than the other, and that is perfectly okay. Many toy users actually practice oral sex on realistic dildos as a way of improving their BJ skills, and of course, because it is enjoyable. Doing it together with your partner, at the same time, is one way to spice things up between you two.