Best results were achieved by holding it level and launching using a gentle underhand motion. Once in freefall the wings extend and it will glide (although that might be overly generous) down, landing with a bump that will trigger wing retraction.
The wings as described slow the fall of the device and, in conjunction with the battery counterweight, keep it level and land it in a relatively controlled manner. That said, throwing it from any significant height is not suggested. Initial tests were conducted over a bed, although later flights (shown in the GIF on the first page of this guide) were were successfully conducted onto laminate flooring from approximately four feet. Also, testing it outdoors in probably not the best idea as wind gusts could prove disastrous.
This project is a demonstration of what can be done quite simply with just a Circuit Playground Express and a few other pieces. The result is fairly delicate. A more elaborate (and stronger) arm mechanism could be designed, and stronger servos could be used, both in terms of torque to handle a more complex arm, as well as using one with metal gears to better mitigate stripping. Some sort of feedback could be used to stop the servos before there was a problem. All that aside it's a fun demonstration of what's possible.