Velocity is the most important quality of any bird. The ideal bird should have a donut hole from the side view at the start of the roll and turn into a blur as it spins from pure speed of the roll. If you can count the spins at all then bird has low quality. Great Velocity is the only quality that you can’t add, if the birds don’t have it you can’t get it later….
The best depth is 20 to 30 feet. Less depth then 15t feet and the birds don’t stand out. Birds rolling over 35 feet tend to be slower getting back to the kit and roll slower.
Good birds should be rolling at least once or twice a minute or more. Birds rolling less then once a minute and you are losing scoring of points during competition flies.
Quality is more on style, are the wing up and not out to the side (H-Pattern). The bird should start the roll and end the roll quickly and end in the same direction.