The may require a little tuning to avoid vibe, but it does function well.
Let me know if these pics don’t really cover what you’re looking for:
While not completely interchangeable with it, it’s like an updated version of the old Buzz-On SPR system. In fact, let me try something…
Nice! With a long enough axle, and some way to center the spacer (in the case of the Menehune, that’s the existing SPR seat and axle), it will work in yo-yos that were set up for SPR.
(I can’t just slap one of these into a Profly like I could an SPR because the axle isn’t long enough. Also, the raised area on the back of the SPR fits snugly into a recess in an SPR yoyo, so it’s centered a little more securely. A clever person could probably produce a washer that converts the stem recess into an spr bump.)