The Pick Up attaches to the top of the bass with some green stickum that looks and feels a lot like silly putty. A little tin is supplied that ought to last for years. It's reuseable and I have tried the PU on several basses, all with the same dab, and it hasn't degraded so far as I can see. The great thing is that one PU can be used on a multitude of instruments as it only takes seconds to change. This PU is actually a voice coil system, a type of microphone, which is well insulated from ambient sound and not unsurprisingly, actually sound like the bass! It is actually intended to be used in a studio environment, but my customers are getting good results on the stage. The sound quality seems to be without peer, though there is a volume ceiling a little short of some of the competitors.
There are three components in this system; the pick up, the XLR cable , and the pre amplifier. The Pick up sells for $595. The package is $750. I usually recommend the 4 channel PA mixer that a famous retailer/online supplier sells for $80, as I use something similar (but more expensive) with fine results.

The Amplifier is a self powered, bi-amped unit which can sit on a stand as though it were a PA speaker. Which it essentially is. It's got almost 300 watts and is incredible tight and clear. Two of these, a mixing board, and maybe a reverb unit would be adequate for an entire band as well as the bass itself. The box is 11" wide, 14 3/4" deep, and 15" tall. How many could you put in your trunk? $700.00

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I use the Acoustic Image Contra on a regular basis with great reviews from all observers. They make a variety of models these days, starting at $949 for their minimal (perfectly adequate) combo. Mine has been absolutely reliable for almost 3 years now, and has enough volume for small club volume rock, despite what I have read elsewhere. For doublebass, it rules.