The SansAmp Bass Driver DI (BDDI) has been hugely popular for very good reason: when used properly, it can sound great. Since not long after it came out pretty much every major recording studio has had one, many live sound techs have carried them. Nowadays there's a ton of competition for the BDDI, but it was The One for a long time. Matter of fact the reason I heard of the BDDI decades ago was after a bassist friend's band did an album for Interscope in a top L.A. studio. He said the studio recommended the BDDI, so he used it, and loved it.
The BDDI's immense popularity doesn't mean everyone has to like it, and no device will please everyone. However as noted by many, it's not intuitive and some give up on it too quickly. For example:
- Treble and Bass are cut/boost, but Presence is boost only
- Treble and Bass are post-OD, but Presence is part of the tube emulation: turning up Presence will increase saturation (overdrive/distortion)
Some say the BDDI is too clanky, but I believe that comes from users setting all EQ controls to noon
including Presence, because they think that noon is flat. As noted, noon is flat for Treble and Bass, but Presence is boost-only, so setting it at noon will result in lots of hi-mid boost -- i.e. "clank".
Also, the sample settings in the manual all have Blend set fully wet. The biggest tip to the BDDI is "Blend is your friend". If you think the sound is too mid-scooped, set Blend at noon and tweak from there. Also as noted by others, you can enhance mids by rolling treble and bass back. Finally, I'll add that many bass amps are scooped by default, and/or have mid scoop contour controls (such as the Ampeg "Ultra Lo"). That's because scooping some mids often sounds great... but adding BDDI scoop to Ampeg scoop can be too much of a good thing.
It's great that we have so many choices these days -- in fact I have a bunch of preamps in addition to the BDDI -- but the BDDI is legendary and rightfully so.