It's worth noting that the developer now lists this as "abandoned" on their website. As it currently exists, this completely bollixes Ableton Live in versions from 10.0.1 thru 10.1. If you'd like a VST that automagically hangs your entire DAW, this is for you...but I'm betting that that won't hold a lot of appeal for 99.999% of users.
Having used the real thing many years ago, I can say pretty safely that this behaves the way it should. It's a 'broad brush' approach to EQ; those expecting to find a tool to make wild, radical changes might want to look elsewhere. But for those who want a device that reliably 'nices up' signals without imparting anything extreme, this is your go-to. Hell, it's my go-to, actually...I find it winds up on my master bus all the time as an 'I don't even need to think twice'-type of choice for zeroing-in overall spectral content. It also has a few frequency settings not present on most other Pultec emulators, which is a big plus. You can't go wrong here.
This simply works, period. On occasions where DC offset gets introduced through effects processing, or as part of the original signal, Doffset works totally transparently to strip the problem aspect of the signal out. Other than that, it does nothing...which is precisely what you want! I've reached for it numerous times when a rogue plugin has generated a DC offset, and every time, it gets the job done. I'd describe it as pretty essential for those who do a lot of sound design, heavy mix processing, and the like.