I used the Seymour Duncan SM-1N and SM-3B as replacement pickups on a Violin Bass (Beatle Bass), inspired by a Seymour Duncan Blog article 'SD Mini-Humbuckers and the Hofner Beatle Bass' by Jon Moody. Under the cover, these pickups have a 'blade' rather than pole-pieces, which means they function properly with four strings.
I'm very happy with the outcome, though fitting them was not straightforward. I had to use new mounting rings, which proved awkward to install on the Harley Benton instrument. And I wanted to be able to select series or parallel in 'both pickups' mode, and finding a hum-free wiring scheme took some research and experimentation.
Nevertheless the bass now sounds marvellous, with a rich and accurate bottom end, and a smooth but detailed top end. It may seem counter-intuitive, but these are lovely bass pickups (though be sure to check your string-spacing).
They were a fiddle to fit, but totally worth it!