Saildog is absolutely correct about leaving it unattended. But if you're stuck motoring in calm weather with plenty of sea room, it will keep you on track. I have ours Garmin 128 nmea connected to a RayMarine 6001 autopilot and it works fine.
Some issues you need to be aware of before you go to great expense. When you engage Track on the autopilot, it will drive the boat to make a 20-30 degree course correction to get you immediately on to the track. It can be quite a surprise as you try to figure out where it's taking you. This happens even if your cross track error is only a tenth of a mile. Then it can take up to ten minutes of snaking through the water before it finally settles down. You really don't want to use it under sail.