Locking tuners on bass don't really make much sense unless you've fitted a bass trem. Even then, the principle used on guitar strings won't work well on much thicker bass strings. Locking tuners work by having a hollow shaft with a pin in the middle that is screwed (either from the top or the bottom of the tuner depending on the design) so that it presses into the string as it pokes through the cross-hole in the tuner, and deforms the string into a U-shape within the tuner, with a lot of pressure acting on the string where it's caught between the pin and the internal sides of the tuner cross-hole.

With much thicker bass strings, especially the E and A strings, I don't think you'd get enough deformation of the string by the metal pin for the string to be held firmly enough not to slip.

So if you do fit a bass trem, provided the trem has fine tuners, then a locking nut is the best solution.