Haven't shot with it yet. Just from trying it out, no tunnel effect, but it is a little different than an actual scope since there is no magnification; that makes it easier to acquire without having a perfect sight picture (meaning eye position relative to it can vary a little more than with magnified). I've moved my head forward and back and it seems to maintain position fine, but without the front post, it would be impossible to tell what you were aiming at because you do get canting. Only took a few minutes to tweak it to align with the current sight setup, but will have to go shoot to dial it in fully. Need to get a fold down rear sight now.
Will either order or pick up a Magpul this weekend, I just flipped up the long distance sight on the rear to make the dot easier to see. I bought weaver offset rails because I didn't know this one came with the cantilever mount which is intended to allow the addition of a magnifier even without a full length rail. You can adjust the intensity of the dot so it essentially gets "finer" for different lighting conditions. The highest setting is too bright in everything but direct sunlight, but making it a little dimmer sort of makes it easier to acquire too, at least with two eyes. With one eye, I can dial it almost all the way down and still see it fine. I like it so far.
