Thanks for the reply. You satisfied my curiosity on estimated cost and impact upon the drone. Amazing what can be done to enhance the solo and I'm sure that future modification will follow.
I remember adding a device to my fixed wing trainer to maintain level flight and altitude. It was expensive, and worked on the principal of seeing the horizon and maintain level flight based upon the difference in proportion of dark ground to light sky. I'm sure the controller had a barometer plus other devices. Worked great. I was able to teach a lot of new pilots by starting them on this before weaning them off of it.
As I said, it was expensive, and big. It had a controller, a sensor pod to sense the horizon and a distrbution board to connect the controller to the receiver and aircraft. The point that I would like to make is that a short time latter new products became available which were cheaper and smaller also and worked great. Consequently, I like to wait before I try out any modification to make sure it has an advantage I really need and if the technology and cost are reasonable.