There are two bass pickups from Fishman that I like, the BP100 and the Full Circle. First, the BP100:
This was one of the first pickups developed by Fishman. It is designed to clip two piezo elements onto the bridge of the bass, using two metal clips to apply the required pressure. The output jack then clips to the strings behind the bridge. When this pickup was introduced, many players had problems with achieving the best possible tone and the pickup developed an undeserved bad reputation. This was entirely due to mis-application and improper usage. I was using one myself and through experimentation achieved a great tone and sound. I still use this pick up today on my classical bass when I need to amplify it. The keys to a successful sound with this pickup are to fit the elements carefully to the front of the bridge and to use the proper pre-amp. Most bridges on double basses are curved slightly across the front which prevents the element from full contact, which is critical. By flattening the face of the bridge beneath each element, full contact and signal can be obtained. Once that is done, running out to a Fishman BA2 or a Pro-Platinum EQ pre-amp will provide a full rich sound that is great for pizzicato playing.
The Fishman Full Circle, developed within the last few years, was a breakthrough in double bass pickup design. Most basses are fitted with adjustment wheels in the bridge which allow the player to raise or lower the action of the strings. Fishman incorporates the pickup element within the adjusting wheel body and the result is a rich, full warm tone, especially good for arco playing. It can be used without a pre-amp, although using one will improve both tone and flexibility of sound. The only downside to this pickup, if it can be considered one, is that it requires taking down the bridge in order to remove it. Most players choose to leave it in place; the effect on the sound of the un-amplified bass is minimal.