After some use I still think that as a more traditional compressor (read: single band), it works very nice. It is a big step up from the old school pumping compressors. I did a very long study on compressors for guitar and bass, because I will use it on both. Knowing I'd use a little compression all the time, I'd surely shouldn't mess up my preciously build sound. The Diamond Bass Comp actually did fade away the nice twang of my bass. But it is smooth as butter and very musical. On low settings, it just gives a little invisible punch to the signal, pulling it into presence. On higher settings it gets more aggressive, but always with smooth character. If you hear any pumping, ensure the volume INTO the pedal is correct. When it's very high, the compression gets a bit strange due to threshold level not being on par with the input signal. I noticed this when my EQ before the compression was pushing the levels a bit to much :) My bass has a hot signal, but the Diamond is not bothered by that much. I was also thinking about the Empress, with more options, but I'm very pleased with the simplicity of this pedal. Less tinkering, but 100% good sound.
EDIT - I finally switched to a TC Electronic Spectracomp and it outperforms the Diamond for sure.. It can do ANYTHING you want. Especially the multiband compression makes it so much more uncoloring and more stable and smooth in compression.
I play a 60s Fender Jazz into a Yamaha G100 head into a Glockenklang Tedd cab. No need for changing this...
Used to own this unit. Love how it is user friendly. Intuitive knobs. Transparent sounding compressor and shines with fingerstyle. But the diamond does not offer a spectrum of compression ratio. Issue came when I needed more attack for slap/pop and the diamond was lacking.
Another consideration for potential buyers is that this requires 18V power. The power adapter that was bundled with this unit was faulty and I couldn't pass it to my friends to try (as they didn't have a suitable power supply). There's no battery compartment. This takes up some space on a pedaltrain mini. I use a Roscoe SKB (Ash body + maple neck) with 18V active preamp.