No, so I can't comment on that.
Compare before you buy - it's much less powerful than Keypower's ATX PSU and not much cheaper.
It might look smaller 'cause it's not cube shaped, but almost 8 inches long.
Edit: I just found out that it's a good match with their SleekLine enclosures though (which in turn is a good match with FlexATX motherboards like FV24 - if you don't want to/can't build your own case)!
In case you contact them, ask if they are selling the SleekLine+ case with this 12V DC-DC PSU instead of the mains one. I would love to have one of these in my trunk.
when you are using an inverter to power a mains PSU you have to calculate the overall efficiency of the system by multiplying the two efficiencies.
For example if you use an inverter (with let's say efficiency 65%) and a mains PSU with 80% (propably with less efficiency - closer to 65% - I don't see why an AC-DC should be more effient than a DC-DC commercial PSU) the overall efficiency of the setup that supplies your computer should be: