Overall, this pickup set has its own reputation and reviews could be found all over the internet. Thus, ? will not be talking about the tones of the pickup. I would like to focus on the physical aspect of it.
First of all, I gave quality 4 stars because of the QC that Seymour Duncan apparently did not really gave thought. My Nazgul Bridge pickup had a dried chunk of wax potting between its coils. It required me to peel it with a needle but a thin layer of yellow wax residue is visible. Mind you that this is all up to Seymour Duncan as the package was unopened and I, myself broke the seal of the box.
Secondly, they have huge polepieces. I have installed these to my RG1527 which used V87/V77 pickups. Nazgul/Sentient require 6mm more clearence than the latter set. If your guitar is using a vintage/vintage-hot output pickup, chances are you will need additional drilling. Though, this is not a drawback about this pickups. This is fairly normal for a passive contemporary pickup. Same issue would also occur with Bareknuckle Aftermaths etc.