I use this shower from the back of my Toyota RAV4 for cleaning up after surfing and after a day at the beach with my family. I used gravity type showers in the past which have their place in outdoor life but as long as I have a power supply this is the only shower I need. I bought an extra one so I have a back up in case of any unforeseen mishaps. When I'm working I sometimes stop to surf on my way to work when waves are good and this is the best way to shower after being in the ocean that I have found.
I love this shower. I live in Northern California and surf often at dawn before work. This shower let's me get warm and clean up before heading into the office. Before, it was either a cold shower or I was carrying a large jug of hot water and trying to pour it over me.
This shower is more expensive than the pump style models but I think it is worth it. It is super convenient, works great and has a great sustained flow. All the other surfers in my favorite spots are envious.