Looks a nice bit of kit that - however, it does say for "Wet or harsh environment" - not for underwater use.
The two are very different environments. A wet environment might be, for example, a bathroom. Places where contact with water is likely, but won't be 24/7 underwater.
When underwater you have additional water pressure to cope with, which gets relatively high pretty quickly. The seals / enclosure of this might not be able to cope with continued underwater use. You'd want something that was completely potted and encapsulated, and I don't know if that is or not.