Yeah, I use mine all the time when I single hand... If I have crew I don't usually hook it up... the most important thing I can pass on to you is to make sure you've balanced your rig... that means you absolutely must know how to properly trim your sails for each point of sail. With the rig balanced the AP exerts less effort to keep you on course, which will give you a lot more confidence and will probably use less battery.
I don't have a wind sensor on mine so I have no comment regarding that. Therefore, if the wind shifts, I'll either trim sails or change course.
Under power the AP is quite useful but it really shines when you're sailing singehanded because iit frees you up to trim sails, eat, toilet, read, whatever...
Downwind sailing can be somewhat erratic, but you really need to experiiment for yourself. The problem is that the unit may over correct for the yawing motion common to downwind sailing in the oceran, and may set up an accidental jibe....... not good. But downwind on flat water, such as when I come back into the bay, I can set up the AP to handle the boat while I start putting things away....
Last comment... WEAR A HARNESS and TETHER... and stay ATTACHED to the boat at all timesl when you singlehand with or without the autopilot on.