I used sansamp stuff for years--the bass driver DI, the rack-mount RBI, and a I still have a para driver. IMHO, it's not a good choice for double bass.
The sansamp stuff was initially designed to imitate the overdriven sound of a tube amp, and it does a good job of that. It has very powerful active tone controls, so you can do a lot of extreme tone shaping, which is good if you want to sound like another bass player or a different bass--if you want to go from James Jamerson to Chris Squire to Marcus Miller, say. But that's not usually the sound you want with double bass. I generally want a very clean, very flat, uncolored sound. My bass has a great acoustic tone--I want that tone, only louder. The sansamp "colors" the sound a lot--it tends to have a really pronounced mid-scoop, and to my ears the high end is grainy and harsh. The para driver has a mid control, but I still find it really hard to dial in a full, pleasant sounding midrange. I bought an avalon U5, and the first time I played through it the sans amp was retired for good.
Sansamp stuff is rugged, well made, and well designed. It sounds good if you want 80% of the tone of an Ampeg SVT with .1% of the weight, or if you want a lot of dramatic tone shaping and put range over sound quality, or if you want to add tubey-sounding dirt to yur tone. It's not expensive. But there are better units for double bass available for the same price. The Fishman ProPlatinum for Bass is excellent--it has a variable high pass filter, 5 bands of eq, a compressor, and a DI, and it sounds much much better to my ears than the sansamp. It's not as good as the Avalon, but it's better suited for double bass than the sansamp
just my opinion, others may disagree