As an instrucor I did never allow my students to use self-draining snorkels or masks. During training you want your students to become confident with the manouvre of evacuting the mask and the snorkel.What’s the issue with self draining ones?
And this is for prooving they have got good control of the valves inside their skull and controlling the airways.
For me the snorkel has always been a powerful didactical tool. Then when scuba diving I do not generally carry a snorkel with me.
But for a novice, starting his first course, owning a snorkel (the simple model) is required, as the instructor will use it for a number of exercises in the pool: for example swimming while breathing through the snorkel and without mask, or evacuating the snorkel after a small free dive.