Will be interested to hear how it goes we also use the 12v one and I find the power thing a pain. I have been eyeing off the ironman one that you charge the usb when driving.
The Ironman one for all intents and purposes is the same as the Jaycar model.
OK ... gave it a charge and dropped it into a sink full of water. The output seems identical to the 12V wired one, so all good there.
The impeller is driven by a tapered spindle (as opposed to a D shaped one), and our 12V one also has a tapered spindle (purchased from Whitworths). The only issue with a tapered spindle is that sometimes the impeller wants to slip down the shaft and not spin. Its easy to fix, simply open the bottom of the pump and push it back. A bit of loctite would probably help circumvent the issue too.
Now ... the good thing about the tapered spindle is that the impeller won't split under pressure, as it would if seated on a D shaped shaft.
We're heading away in a couple of weeks for a bit of rest and relaxation, so the shower will get a good workout then.