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I've had them on two guitars, one with a Bigsby vibrato and one with a fixed tailpiece. I think the main advantage is with a vibrato tailpiece, since it reduces friction at the contact points of the strings & saddles, helping to maintain tuning stability and reducing string breakage there. But if you do a lot of manual string bending, I would expect the same advantages.
If you're thinking of adding one to a guitar, be aware that some roller bridges have fixed saddle placement, so intonation adjustment isn't possible.
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