The documentation says 122m with clear line of sight but I don't get anything like this as I'm having to measure the piezo sounder output to determine distance, which proves not to be too accurate as the distance increases. I calibrated the signal up to about 6m. I really need to find where to take the feed that drives the sounder.
To be honest, I got it into my head that servo's were for spinning so thought steppers were the best bet for this project. You can see though that the movement is not that smooth so when I get some time I will see if it works better with servos.