ABT/Trac, as far as I know, are the only fins that will center themselves and positively lock into position. That is a great, and very clever, feature. There is a spring loaded pin at the center point that is held in the out position hydraulically. If the system is turned off, or should fail, the fins will hydrodynamically center and the pin will lock them into position.
I cannot imagine trying to put in a locking pin manually in a big sea with flailing fins.
Also, they are well supported and extremely well built. I have them on my boat, and if I may say so, I made a very wise decision selecting that brand.