I bought Trilian only because I lacked a good acoustic bass. I wasn't at all interested in the synth basses it offers, as Zebra can perform that duty much more efficiently. I also didn't care that I could pull up Trilian patches in Omnisphere.
However, after a couple years with Trilian under my belt, I find I'm using it more and more, and not just the acoustic basses that I originally got it for. There is an instrument called Hardcore that I really like for heavier genres. But still can't get excited about the synth stuff.
I have two complaints re Trilian. First, the samples are huge and take a long time to load. Second, it's not as easy to program as a good Kontakt library. If I'm going to feature the bass prominently with lots of articulations, I'll usually fall back to one of my old Kontakt-based favorites such as Orange Tree Samples' awesome Rickenbacker.
Trilian's integration with Omnisphere is kinda OK. I hate clicking on a patch and not realizing it's a Trilian patch until it becomes obvious when the "loading" progress bar takes forever. Same thing with loading Keyscape patches within Omnisphere. There are a lot of cool possibilities with layering the three Spectrasonics instruments, but I am too impatient to explore them fully.