Quick product test, before dashing out the door.
Open the package, looks fairly straight forward. Put the unit under the tub faucet, and fill a bit with cold water. Instructions say cold water only. (Water cooled pump, most likely.)
Took it out, and plugged the unit into my battery jumper pack, using the 12 volt lighter socket.
Leave the nozzle off, pump some water back into the tank to purge the air out of the lines. Switch off. Nozzle on.
I like it! The straight spray breaks up after a few feet, no surprise. The unit allows me to spray water on the roof of my trailer (from standing, nozzle about waist high). Or horizontal, the length of my van. I'm not all that sure either of those are useful.
The real test, is the condensing unit that's scrap left over from another project. I used the sprayer to rinse out a refrigeration condensor. Worked nicely for that. And then tried it on a central AC condensor coil. Did a reasonable job there. Definitely not a power washer, but about the same as a low power garden hose. 3.5 galons of water won't rinse out a cental AC condensor, but it's plenty for a couple of refrigeration coils.
The adjustable nozzle also widens out to about a 30 to 40 degree fan spray, which would be useful (as the one person who commented said) for cooling down a hot doggy after play time. 3.5 galons won't wash an entire house, or a deck or something. But sometime when you're away from the garden hose, that can be useful.
I'm very pleased.