Reference 4 solved some last 10% issues in my mastering room. I had a 46Hz null/dip in my frequency response that Sonarworks corrected, smoothing out the low-end. I'm using Egglestonworks Andra IIs powered by a Pass X-350. I do have some recommendations for users on how to improve your own results. For example, no single subwoofer. Reference 4 cannot realistically measure where it is and compensate for it (at least, from what I've researched). I would like to see the ability to manually set Gain level by typing it in, or Holding Shift while adjusting it to slow it down. I would also like to see more curves, such as the Bob Katz' 1Khz pivot curve (flat from 20Hz-1Khz, then linear roll-off from flat at 1Khz to -6db at 20Khz). Pros: Inexpensive, accurate, easy to use/measure Cons: Too easy to mis-measure for accuracy, and little best-practice documentation NOTE: Systemwide will not tolerate multiple DAW's running simultaneously in Windows 10, and will crash if you change your sampling rate in one of the DAW's.