The "+" discs (both Teebird & Roc) feature a sloping rim wall instead of square. The angle where the flightplate meets the rim wall of the wing is obtuse instead of right, resulting in a "beefier" (and many would say uncomfortable) feel.
IMHO, they feel completely alien & nearly ungrippable in the hand, so much so that one would have to fly into the basket every time, come to rest, then levitate up & magically fly back to me, lovingly tickle my tween, and gently nestle back into its rightful place in my bag for me to even remotely consider putting one in the bag.
