I should sell this pick-up?
Bats,
If you can afford something else, it would be a very good investment.
The Fishman BP-100, that you have is a awful sounding pickup IME, I used one for two years and gave up on it. It requires that you use a 10 Meg Ohm Load, to get a decent sound, and the installation of the pickup has you put two clamps on the bridge to mount the piezo discs, which then act just like a mute, interfering with your basses sound production.
The Realist, Realist Life Line, Fishman Full Circle, and even the Underwood, all sound infinitely superior. My pickup of choice is the Ehrlund EAP and Ehrlund Pre Amp, it's equally good playing Arco or Pizzicato, but you'd have to test one on your bass, to make sure it works. Since the Ehrlund is designed and manufactured in Sweden I'd recommend contacting Goran Ehrlund to see if you could arrange a trial of his pickup. He used to offer that option. Invalid Link Removed
The Schertler StatB is also a good option.
Your amp looks to be one of the original Roland Bass Cubes. I owned one, and liked it, for low volume settings it has a decent sound.
Ric