those tuners, as with all tuners, should be fine. Technically speaking tuners cannot slip. Look at the picture below..
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the strings are attached to a shaft connected to the round gear, that gear cannot move unless the tuning peg is turned and that round gear is driven by the tuning peg shaft. As long as the bass is strung properly and tuned 'up' to the note (rather than down, which leaves a difference in tension in the string either side of the nut) then the tuners should hold fine. From what i can tell the only reasons to change tuners is weight, accuracy (more precise ratio's) and cosmetics.
......back on topic, i should hopefully be joining very soon, when my new pickup arrives to put in my refinished bronco bass