Whoa, there's a misconception with EMG HZ's. Those that play metal and such dog on them as a whole. Did they not know that there's different kinds of HZ's? The HZ 3's for me were horrible. Most flat sounding pickup I've ever heard. Not much of a high output high gain pickup. HZ 1's have the least output of the HZ line. More vintage sounding. The HZ 4's is where its at. It pretty much screams and give you incredible crunch and cuts through on solos. They do sound a bit thin, but its pretty much modeled after the EMG 81, which also is a thinner sounding pickup than the 85 as I think the 85 sound a bit too fat for my tastes. I guess everyone has their opinion on what's thin and what's fat sounding to them. I did not find the HZ's muddy and too thin at all. I play aggressive metal and I usually demand high gain from a pickup and the HZ 4 is one of my favourites. I really can't speak for Robot and Rex, as I'm quite suprised with their outcome of their HZ 4 experiences.
I also noticed that the users on this thread that don't like the HZ-4 ended up liking the 85 I'm guessing for "beefier" and bassier tones. Although the 85 has more balls, it was just too thick for my tastes..and the bottom end is too fat. I wanted the 81 sound, but with the brutality of the 85 so I ended up getting the SD blackout.
I still rate the EMG HZ-4 as one of my favourite all time passive pickups and I've tried virtually the whole Dimarzio line and most of the Duncan line.