I'm a "certified" wind installer for residential wind power.
Know how many installs I've done? Zero. Why? Because I refuse to install it over solar in most residential circumstances.
I read their FAQ and have some concerns:
Can my battery get overcharged? Voltage does not overcharge. Too many amps coming in for too long will overcharge a battery. This is simply not possible with a micro turbine such as the Windwalker 250. Think of the Windwalker generator as a “trickle charger” for your battery or battery bank.
Yet this is a device that can put down 30 volts * 8 amps = 240 watts. Assuming they step down the voltage, 8 amps is no trickle charge. No indication of a charge regulator. With that kind of output, it could easily overcharge if you had sustained high winds.
What if I want to check the generator’s output?
First disconnect any load (such as the battery). Then connect the +/- probes of a digital multimeter set to DC voltage directly to the output wires of the turbine. While it is spinning, you will get an accurate voltage reading.
This won't tell you how many watts or amps it's producing. It's horrible way to measure.
No information on what wind speeds are required for what output.
Also these devices are "wild" alternating current. They have to be rectified to DC. They're mechanical, so they are much more likely to fail than a 240 watt solar panel.... Technically, it'd generate power in a high wind condition where it's cloudy and solar isn't available, but I'm not sure I'd go for it.
My advice - spend the money on a similarly rated solar panel.. It'll cost less, produce more power reliably (subject to sunlight) and be a lot less maintenance hassle.