I have the pins Domino, and I have these spacers. I think they’re fantastic. Just as with the pins, you can work without having to measure specifics. Just attach a spacer and go to town. You *do* have to remember to move the spacer from one pin to the other when you switch parts. But it only takes a second.
They are nicely machined, have a magnet in them, which holds them in place on the pins. One of the first things I got from John and I would definitely buy them again.
The only thing I would change, is to engrave the sizing / offset onto the face of the these. I plan to do this with a Dremel or something, so in the meantime I wrote on them with a Sharpie.