I'll start with the conclusion so you don't have to read me rambling if you don't feel like it:
This is the best EQ equipment I've ever used! It is by far the most important tone-shaping piece of gear that I have. If you have problems with your tone like muddiness, harshness, too much or too little something, this is the tool you need to try to fix it. I greatly recommend it!
Some 25 years ago I bought a Boss GE-7, that was my first experience with an EQ pedal. I'll be blunt, I hated it. I found it noisy and hard to set up to get a usable tone, I sold it a few months later and basically gave up on EQ pedals.
Fast forward to today. For all these years, to me, EQ was just the 3/4 bands on the amp and the tone/s on the guitar/bass. I made do and was quite satisfied with the results for a long while until I started noticing that some of the tone issues I was inevitably having were starting to annoy me greatly.
I have a couple of Cort basses (B4 fretted and fretless) that I love. They feel absolutely great but the sound of them is not that good. The active preamp sounds very sterile and uninspiring to me and the passive sound, although quite nice, lacks power, big time. To complicate things a bit more, I love flatwounds but I also love a well-defined sound.
Well, this pedal fixed all my problems. I now just removed the battery out of my basses and play them passively using the very transparent clean boost and the tone shaping of the EQ to make my flatwounds sound more defined. It somehow keeps the basic tone of the instrument while solving the annoying inherent problems.
When it comes to guitars, I am definitely an active pickup enthusiast. All my present guitars have EMG's in them in 9v and 18v mods. I find that they work very nicely with the paraEQ MKII. One of my guitars, a Cort g300 has a basswood body that I found way too muddy. It came with a seymour duncan set that sounded quite good clean but got muddier and muddier the more overdrive/distortion was introduced into the loop. I then decided to replace the pickups with an 81/60 EMG set. This helped a bit but didn't fix the problem by any means. It took the paraEQ MKII to fix it and it did so brilliantly! The 3 bands of the paraEQ allowed me to remove the mud, and improve the definition and bite of my guitar. The level of articulation with heavy distortion is just impressive, every pick attack counts and sounds great.
Last but not least, I have to say that the user manual is brilliant! It is, honestly one of the best things about this pedal because it is very clear, easy to understand, and result oriented. It gives you some "basic" settings and explains very clearly what frequency to shape and how to do it in order to solve your tone problems. It even has a "my settings" section so you can write down your own settings. It only gives examples for electric/acoustic guitar and bass but the pedal can be used for probably any instrument you can imagine, it is clearly a "Swiss army knife".
I'll stop rambling now and give a simple conclusion: Although the price of this pedal is quite high, it is worth every single penny. This is an incredibly powerful and transparent tone shaper. The headroom is great, the shaping possibilities are endless and the overall quality is outstanding. If I really need to nitpick and found a con, my fat fingers have a hard time handling the tiny little black knobs, other than that, this is quite simply the most important pedal I own. To me it is way more than just another EQ, it is the ultimate tone problem solver.