The bond is the material holding the diamond. It decides how long a grain stays in the tool and when it releases. Pick the wrong one and the tool either wears out fast or glazes over.
Metal bond
Holds grains hard. The block keeps its shape, stays flat and lasts. It runs cooler under load and pulls less power from the spindle. The trade-off is that it needs enough pressure to keep cutting, and on very hard material it will glaze if that pressure is not there.
Resin bond
Releases grains sooner, so the tool self-sharpens more readily and gives a finer surface at the same grit. It wears faster and loses shape, which on a flat polishing line means more block changes and more variation between heads.
What we actually ship
Metal bond on Fickert blocks and horseshoe segments, because polishers want flatness and uptime more than they want the last few gloss units. Steel-plastic composite bodies where vibration is the problem. Elastic bond for profiled and curved work, where conforming to the shape matters more than holding a flat plane.
How to choose
If your complaint is tool life and flatness, go metal. If your complaint is finish at the fine end, tell us which grit you finish at and we will say whether a different bond helps or whether you need another head.