The device itself is nice and as others commented you will need a quite substantial wind if you want to produce significant amount of energy. That said, there are a couple of additional issues:
- to get good amount of winds, the turbine needs to be high and a 30' to 45' pole costs much more than the wind generator itself
- you might need an authorization from the town if you want to install such a big pole (some might not even allow it)
- keep in mind that when spinning the turbine generates a significant amount of noise and vibrations (increases with wind speed). We tried to install one on top of a building at work and the ceiling of the last floor was vibrating at a point that lights were shaking. So you definitely don't want to try that on your roof at home.

Note that this thing generates DC current and if you install it far from your house, you will need expensive cables if you don't want to lose too much by the time it reaches the batteries and inverter. If you want to store the batteries outside, note that depending on the type of batteries, they won't charge in cold weather.

UPDATE:
- I took the wind turbines down after 2 years. The overall experience was pretty negative besides the noise and other annoyances. The total production per turbine per year was 1.5KW of usable electricity which is basically nothing (as a comparison I produced 75KW with 6 solar panels in March 2013 with bad weather).
- We have mostly gusty winds that do not pair well with these wind turbines plus the integrated charge controller is not good enough which leads to peaks up to 17V sent to the batteries in case of big wind gusts. That will damage your batteries or other equipment if you are not careful.

My location in western MA (on top of a hill) did not work for these wind turbines and solar panels have proven to be a more cost effective and reliable way of producing clean power. The noise generated by having these turbines within 20 feet of the house proved to disturb our sleep in the long run. We realized that when we finally took down the turbines.
The device itself is nice and as others commented you will need a quite substantial wind if you want to produce significant amount of energy. That said, there are a couple of additional issues:
- to get good amount of winds, the turbine needs to be high and a 30' to 45' pole costs much more than the wind generator itself
- you might need an authorization from the town if you want to install such a big pole (some might not even allow it)
- keep in mind that when spinning the turbine generates a significant amount of noise and vibrations (increases with wind speed). We tried to install one on top of a building at work and the ceiling of the last floor was vibrating at a point that lights were shaking. So you definitely don't want to try that on your roof at home. Note that this thing generates DC current and if you install it far from your house, you will need expensive cables if you don't want to lose too much by the time it reaches the batteries and inverter. If you want to store the batteries outside, note that depending on the type of batteries, they won't charge in cold weather. UPDATE:
- I took the wind turbines down after 2 years. The overall experience was pretty negative besides the noise and other annoyances. The total production per turbine per year was 1. 5KW of usable electricity which is basically nothing (as a comparison I produced 75KW with 6 solar panels in March 2013 with bad weather). - We have mostly gusty winds that do not pair well with these wind turbines plus the integrated charge controller is not good enough which leads to peaks up to 17V sent to the batteries in case of big wind gusts. That will damage your batteries or other equipment if you are not careful. My location in western MA (on top of a hill) did not work for these wind turbines and solar panels have proven to be a more cost effective and reliable way of producing clean power. The noise generated by having these turbines within 20 feet of the house proved to disturb our sleep in the long run. We realized that when we finally took down the turbines.