I bought this to replace the original belt that came with my t4c. After 14 months, one of the clips that snaps the belt into the electronics disk broke off, and the old belt would no longer work. So I ordered this new one.
I realized, upon receiving it, that I really only needed the strap; the belt includes a new electronics disk. So I unclipped the new belt from its disk, snapped the old disk into place, and didn't have to worry about pairing a new disk with the watch. Now, I have to hope that if the belt breaks again, it'll be in the disk -- since I have a spare.
The new comfort belt is obviously tighter than the old, and seems to start getting readings faster -- I guess 14 months of use stretched it out, so it might be good to plan to replace the strap after maybe 18 months of use, anyway. Get more detail about Suunto Comfort Coded Heart Rate Monitor Belt (Black).