Fundamentally, the technology used on the Fishman and the Underwood are virtually the same. It's a piezo transducer, and the only difference is that the FC places the pickup in the adjuster and uses a passive filter. It still has the characteristics of a piezo pickup. Rev Solo, Realist, Lifeline, PW, Schatten, etc. still all use the same design, where they place the piezo and how they're built is the difference.
Pickups I've tried on the Yammy: PW, FC, Bp100, Rev Solo, Krivo,
Others I still own or have owned in the past: Ehrlund, Dyn-B, Stat-B, Realist, Underwood, DPA-4099B, ATM35, various mics for use on a stand.
For my DB, the BP100 sounds pretty good but I resort to the Realist since it doesn't have grounding issues when I play in louder situations. Otherwise, the DPA4099B is my weapon of choice when possible.
My conclusion is that without the big body, any EUB will come off sounding very nasal. Piezo pickups just make that nasal sound even more boxy. The best Ive heard actually has come from magnetics like Krivo or youtube videos with the mag pups on the NSD CRM4. The best piezo result was actually sticking the Rev Solo where the onboard Yamaha pickup used to be. I had to chisel that slot out to make it fit. Result was still too nasal.
EUBs I've owned in the past: Ergo4, NSD CR4 and maybe I think one other that I can't seem to remember. I've played the Eminence and wasn't impressed either. Soundwise, I agree with you, they're all similar in a way - not that great.
With the Krivo it depends on the physical approach and the EQ settings. I've only had the Krivo for a couple weeks so I'm still figuring my way around it. I notice the EB qualities more on the low notes but possible using a different set of strings than the tapewounds might yield a better result. I haven't had a lot of time to experiment. Of course playing arco with such a setup kind throws everything out the window, which is why I say that a DB simply cannot be replicated without resorting to a cut down version of the real thing (like a CE or Traveler).