I used to have a Realist on my New Standard Cleveland laminated bass. Now it has a K&K BassMax and a Schertler Stat-B. I run these through a Fishman Pro Platinum Bass EQ, a Baggs Para-DI, or a SansAmp Bass Driver/DI, into the FX return of a GK400RB driving a Bergantino HT112 or EA Wizzy 112.
On my bass, it was difficult to get any sort of growling mids or note definition from the Realist, even with a preamp. Both the BassMax and Stat-B have better mids/highs while retaining a full bottom end. I haven't used an Underwood myself, but the BassMax is a cheap (~$90) way to get a different tone that's guaranteed to cut better than a Realist.
I'd have to disagree with your guitarist. Neither the Fishman or Baggs "sucks tone", but I consider the Fishman to be definitely the more neutral-sounding unit (with controls set flat, the pre/post XLR-out tones are identical). The Para-DI seems to have a bit more of a cutting midrange, and its bass control is voiced much higher (80hz vs the Fishman's 30 hz). The Baggs has a preset 35hz hi-pass filter (the Fishman's is variable between 15 and 125hz), and it seems to have a significantly higher output from the 1/4" jack. Plus there's no ground lift switch or pre/post switch for the XLR (possibly problematic if you're using both an amp and PA), and while it has a TRS FX insert jack, there's no dedicated tuner out. Both units have a phase reverse switch, very handy for fighting feedback.
That said, I find the Baggs to be more musical-sounding. The EQ on the Baggs seems more like "tone control" (with the semi-parametric notch and midrange you can get many different sounds), whereas the EQ on the Fishman feels (to me) like you're just adding/subtracting so many dBs at different frequencies. However, with my setup I find myself using minimal EQ (I usually cut a tiny bit of highs/upper mids) and the variable lo-cut and compressor on the Fishman are very helpful
I like both and wouldn't want to be without either right now. The SansAmp BDDI is a whole different kettle of fish--it's much more electric sounding, but I haven't tried their Acoustic DI--which many DB'ers love. See if you can try a Baggs before buying; you should be able to find one used for less than $100. As for the Realist, it responds differently on every bass, but you probably won't get too many highs from it on a laminate.