Prior to this, on my '50s Kay I have used a David Gage Realist for 10 years, then a Fishman Full Circle for 10 years. I briefly tried a K&K Bass Max and didn't care for it, so I thought I'd combine the two concepts that had served me so well in decades past: a David Gage designed element that fits by the adjuster like the Fishman.
This pickup achieves all of my tone goals: some percussive attack, a subtle sense of presence, even response over all strings and registers and not least of all, good balance between pizz and arco. It doesn't necessarily replicate what a condenser mic would do - it does work very well in an ensemble with a nice "acoustic" vibe that doesn't get immediately lost in the mix.
Compared to the old Full Circle, I'd say this is a little more even and a little less raspy but nut surprisingly pretty similar in overall character.
I suggest a good buffer preamp with some high pass filtering for best results.
Realist Lifeline XL
Upright / double bass pickup