I have had a Rutland 913 for about 12 years now and whilst it gave useful power when I lived in the temperate zone it is pretty useless now that I live in the tropics.
pbijim is right, without load it will freewheel with fairly high RPM's but the moment you put it onto load it will stall immediately and this is fairly normal for these units. I have never measured it but estimate that these units need about 15 - 18 knots of wind
before they start even bucking the battery
voltage to put any current
into the battery.
The up side of them is they are very robust and about the only electricals you may have a problem with are the diode bridges which can be replaced for a few dollars from an electronics
part store. The other potential problem is the slip rings which connect the rotating generator to the mount which goes onto the pole. These may need a cleaning
occasionally but I have not had to do it so far.