First of all, I would like to emphasize that I am not an API user. Despite this, I got the chance to use Volko Audio's QA series EQ software recently. Here is my evaluation:
The interface is designed by plain visuals that could be understood clearly on the computer screen. The interface of the software does not resemble the appearance of the original hardware. This makes it easier for the user to perceive it visually. That is, a button that we translate virtually with a mouse, graphically indicating the distance traveled by the button, and leaving the button as a graphical trail. Usually in such modelling software, to see what is happening at the interface (especially on small buttons), we need to lean onto the computer screen. What I liked most regarding the interface is the positive value that this software has contributed to audio and music. Even if you don't buy, you should absolutely try and decide for yourself. It has no downside to the quality products I have used so far in this area. I say, you should absolutely try it.
First of all i used orginal API EQs and i have and 550B clone.I compared with what i hear.It's really aggressive as API EQs.Even only 2dB boost or cut gives you character of real hardware.Tried with kick, snare, overhead, bass guitar and e.guitar.You can get soft or hard effect from these EQs.And i tested with gaussian noise to see curves.It has real proportional Q as hardware.With only 2 or 4 dB you can get punch of centre freq and neighbor freqs.Adding really nice color.With higher gain values, you can get high Q but it's really sounding musical.Normally high Q values sounding ugly but with these EQs, you will get smooth results.These EQs have what orginal hardwares have.