An indication that it's time to replace your pickup is when the guitar starts to buzz, but that buzz stops when you touch the plug barrel. After eliminating the preamp, and ensuring the string pressure is being transferred to the pickup via the bridge, you then need to choose a replacement.
If you already have a Fishman system, then the chances are that by now the older pickups are no longer listed. This was the situation I was recently faced with and after contacting Fishman directly they advised that this pickup replaces earlier versions (though it's always wise to triple-check the dimensions).
Fitting the pickup is straightforward, though you need to be extremely careful not to bend the lead where it connects onto the pickup body as this will damage it. The pickup is supplied in a protective rigid plastic case and my order was additionally very well packed by Thomann.
When used with a Fishman preamp the pickup has a fairly neutral, even response and a very natural 'acoustic' sound without the metallic upper-mid harshness that under-saddle pickups can sometimes produce. The bass is well-represented without being excessive and doesn't overpower the detail in the higher notes.
Overall I'm impressed with the sound this produces.