For my current project, I have non-standard string spacing, pickups with regular pole pieces do not work.
I needed a compact blade pickup - which is where the SH661comes in.
In the prototype phase, this project was built using Artec Hot Rails, which have the advantage of being cheap, I've used them before, and they work well.
But (like many "single coil size" blade pickups) the Hot Rails are quite curved, to match the string curvature of a Strat - I'm running a very flat radius, and the string balance was poor as a result.
Further, the tonal quality of the Hot Rails is not exactly "delicate", tending more towards power than subtlety.
The SH661 has flat rails, which suits me much better and the resulting balance across the strings is much nicer.
They also have a more delicate and detailed sound, with quite a bit more treble and clearer harmonics. Good for this project (though maybe not if you just want to shred...)
The downside is that the output is down compared to the Hot Rails, maybe not higher than a single coil would do. I can feel a pre-amp coming on...
Oh!
And an important point I nearly forgot: The wiring diagram supplied with the pickups seems to be wrong. When I initially wired the pickups, following the supplied chart, there was a lot of hum and the output was *really* low (not just low!) Taking a coil tap into single coil mode, the output was better...
Some testing with my oscilloscope and a tuning fork, and checking each coil individually, indicated that the coils were phasing against each other, cancelling each other. Flipping the wiring got everything working much better (no hum, more signal.)
The wiring that worked (for me) was black & screen to ground, white to output, red & blue together. I'm not using a coil tap, but it would go on the "common" red+blue if I were.