I've read about them and the positive effects they can have, so I followed Gary Willis's online YouTube videos for how to build and install one. Took a while to find the right wood (1/8" thick trim at 3-/2" wide? Good luck; I had to cut down thicker wood), but it's done and now residing on my Sire V7. Bottom line: I love it, and I can't believe how helpful a little block of wood can be for improving your consistency, attack, and speed. So yeah, it works, but I'm not sure I could recommend it for guys who really like to dig in, and it's better suited for J style basses design-wise, due to the PUP layout, since it sits right in between both.
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Gary's building videos:
Part 1: https://www.youtube.com/watch?v=dKffNbWXRfQ
Part 2: https://www.youtube.com/watch?v=rf3ycFvSDQc