Because of a series of spine injuries, I cannot twist to breathe when I am swimming laps so I use a snorkel.  This unit is great in the pool and the purge valve makes it very easy to clear water from the unit.  I had to have my dentist custom fit the mouthpiece due to abnormal bone growth in my jaw, and that was easy for him to accomplish without affecting how well the snorkel works.  I don''t use the clip - it isn''t necessary in the pool; not sure if the unit would work as well in fresh or salt water without the clip.

4 stars because it's good but it's kind of hard to manage it stay up and tight to the mask. No water gets in and breathing easily once you wear it.

You are better off putting money forth on the more expensive model with the curve and strap.
This model is not for the competitive swimmer.