Hmm. . . I picked up one of these for $30 in a D.C. area Costco seems like February (?) So they've been on closeout in different areas for a while.
I've used mine a good bit. It's definitely worth $30. But, for light loads, there may be better choices. Mine doesn't seem to be all that efficient for low-draw use.
My standard test is to run a 13W compact fluorescent off of a 12ah gel-cel until the battery is drawn down to 10.75 volts. I have a smaller 350 W inverter that runs the light for a good 15 - 16 hours. The big Xantrex only goes about 10 hours. On the other hand, it WILL run my 700 W microwave, which a couple other similar units I've tried won't do. The AC it produces isn't exactly on frequency (varies between about 58 and 62 Hz) -- but I guess they're all like that in these days of inexpensive mass-produced electronics.
Also, it seems to work a little better when I've got the engine running -- it likes 14.5 V better than 12 V. (By this I mean it holds up closer to 120 V, with less hash on the output, and seems to stay cooler.)
HTH