I added wing tip drag rudders (like the B2, and X47B) to my Opterra 1.2m after removing the inboard and outboard stock vertical tails.
link to my Spin testing of stock model (mentioned in the video) is at:
https://www.rcgroups.com/forums/showt.... Drag rudders work very well and as expected. more flights will be needed before I start removing the addon centerline tails all together.