I recently bought Trilogy and am satisfied. I don't use synth basses all that much; I got Trilogy mainly for its electric and acoustic basses, and these are excellent. I haven't used Yellow Tools Majestic or EWQL Hardcore Bass or any other competing products, so I'm not sure how Trilogy compares to them. But the sound quality definitely blows away any other bass sounds I've used (with the possible exception of some of the basses that came with my copy of Kontakt).
Very usable basses that will add life and realism to your tracks. Admittedly, it is very hard to create a convincing bass line using conventional synth/ROMplers and sequencers. If you do a lot of tracking that includes upright basses, electric basses, etc., and you find that they end up sounding too MIDI-ish and unrealistic, adding Trilogy to your soundware arsenal will definitely help.
My only gripe is that most of them have very little velocity sensitivity, but this can be user-edited. This is a bit of a pain, having to do this for each patch you want to use.