I've looked through maven C4's and zerotech's side by side, maven B5's and zerotech's side by side, and bushnell 15's on a separate occasion.
The zerotech's are better than the C4's in overall clarity, and the B5's have slightly more clarity around the edges than the zerotech's. The bushnell 15's have less clarity than those three, and seem to have a narrower FOV as well, but I have not compared them side by side with another set of 15's to confirm this.
Below is a photo through zerotech's just before dawn. Actual optical quality is a bit better when looking through them and not handholding a cell phone behind them...
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