Given that I can't find any technical specs such as for battery charging cycles, or number and size of DC circuits, or number of AC circuit breaker positions, or who made it or who will honor a warranty repair, I wouldn't touch it with a 10 ft pole.
You can get a US made Progressive Dynamics PD4045 of known origin, support, and capabilities for about double what the Unknown Elixer is selling for on EBay. Oh, I don't find any authorized dealers anywhere but on EBay. I don't consider that any kind of recommendation for a device that will be the heart of your electrical system.
When I built my teardrop electrical system, I thought I needed to cut costs, and bought a WFCO WF8230(??) on EBay for a similar price. It failed on a camping trip and required 3 weeks for warranty repair. It failed again on the very next camping trip! I removed it and spent the extra money for the Progressive Dynamics converter.
BTW, the converter does not provide 120 VAC power from 12 VDC. To do that you need an Inverter. And search here for advice on running an A/C off a battery.
<Chas>
