I don''t really know if this help. It seems to have the same opening as the snorkel so I cannot see  the benefit of it.

I bought this the same time I bought my snorkel.  I haven't really use my snorkel with out it.  So I can't really compare with or with out, but it has had some great benefits.  I have definitely seen an increase in breath control.  It dose keep a certain amount of water from going down my snorkel.  For the price it is worth trying.  I don't see any down sides to it.  If you are putting in an order for a snorkel get the Cardio Cap too.  Oh and don't worry about it being white and not matching your black and yellow snorkel.  They are Black now.  

Happy Swimming

This device you cannot go without it really get the most out of the use of the snorkel.  Although you have to really push in down on the tip of the snorkel or else you will loose the tip, like i did.  Thankfully i was able to get it back both times.  Just check it before using it daily and push on it to secure it staying on.  Other than that i Love this add-on.

Well worth the price.  I had to go to a pulmonologist for a check and he found my long capacity to be 30% larger than people my age, weight and height.  A year prior that wasn't the case.  That's a WOW for a TRI-athlete!!!

If you already got the snorkel, this will give a more added pleasure. Works your cardiovascular conditioning to another level. I enjoyed the challenge of gasping for air but was able to overcome it after prolonged use. Now it just sits on top of my snorkel, and I do not even know if I can remove it. Recommend this!!

I recently bought this to add to my FINIS snorkel.  If you train for running swimming tri's this set up is great it will train you to function at a higher level on less oxygen.  So when you are actually running in a tri or just for fun you preform better with an abundant amount of oxygen. I have noticed a lot of positives effects from using the snorkel and the cap has really helped my endurance all around