I have a model that I think is called the 403. Its mounted to the top mast of my boat and probably has about a 3 ft span. It does a pretty good job of trickle charging my battery bank when there is about a 10 mile breeze or better. I don't think it produces power until the wind speeds hit 7 mph. While it doesn't produce huge amounts of power it does produce it 24/7 unlike solar arrays when generally only produce well about 6 hours a day. That's probably its biggest asset right there it works as long as there is wind night and day. I think I paid about 400-500 for it and it was pretty easy to install. If your use is light it might be able to keep up . I use it in conjunction with solar panels as well so that seems to work really well for me on my 37ft boat when I am out "blue water" sailing.
Most of those windmills don't operate in over 35-40 mile winds or last long if the blades cant be feathered to reduce RPM's. But if you often have 10-20 mile an hour breezes then it should prove pretty effective for you.