On the face of it, the Sentient may seem an odd companion for the Nazgul, the output is completely different, but it's not just about pure power!
The Nazgul is a low, super high gain, growling beast of a bridge pickup which handles low, dropped tunings with ease. You get great clarity and a not too bass-heavy tone (you don't need a bassy pickup if you're already tuned down an octave or two, right?!). From my research it is perhaps a little underwhelming in Standard, though I have not tried it myself above C#.
The Sentient is a Vintage output baby by comparison, with an alnico magnet (Nazgul is ceramic) and voicing set between classic rock and jazz. The combination is perfect however, with the Nazgul being the chug-master during the rhythm and the Sentient providing soft flowing leads at high gain. The clean tones too are beautiful, in all three positions on my ESP.
Highly recommended for anyone looking for passive pickups to replace ones that just can't handle the metal you crave. Though are they better than the active equivalent? That's for you to decide.
Value for money? Depends on how much you want to sound awesome...