Shotgun aiming devices have come and gone over the years and none have proven effective enough to still be viable.
Effectively shooting a shotgun requires both eyes to be open and in use at the same time. Binocular vision is always best when shooting anything and the minute you close an eye you have lost depth perception and therefore the the data required to calculate the proper lead to hit the target.
One eyed shotgun shooting can be done if you know the lead required for the target at it's current distance. Skeet is a good example, the targets are at a known speed and distance and binocular vision isn't as important but if you try the same thing in the field you'll fail miserably.
Proper stock fitting is the most critical issue with shotguns. With a properly fitted stock (and remembering that your eye is effectively the rear sight) it's only a matter of determining the target speed and applying a lead for distance and speed, which is something the brain will provide.
Save your money for shells and practice.....