There are definitely some pros to the Subnado. First off, the portability is a huge plus—you won't need to struggle with bulky equipment. The battery life, though, can be a bit of a downer. While it's decent, you might find yourself wishing it lasted longer, especially if you're planning extended sessions. On the bright side, the recharge time is relatively quick with Quick Charging feature, so you won't be out of the water for too long.
On the flip side, the Subnado isn't without its cons. The most notable is the aforementioned battery life—it's good, but not great. Another downside is the price; it's on the higher end, which might be a deal-breaker for some.
If you're mostly on water, this is a good additional gear to make snorkeling or just swimming fun. The support from Waydoo is also top-notch. I got my replacement device after reporting a bug in the device's update system.