Using any inverter will use more power than direct to DC/12V. I don't know if all inverters are alike in converting DC to AC/120V, but it's a question to ask. If the little portables are not as efficient, it might be a selling point to installing the inverter to allow you to use the 120V outlets.
Another consideration is the type of power output by the inverter -- pure sine wave versus modified. We have a modified on our sailboat and have fried more than one rechargable battery for power tools. But we haven't fried other stuff -- at least that we know of. They say not to use electronics with modified sine wave, but ***knock on wood*** so far we haven't fried a computer.
Just some considerations in your decision.
