I ordered one of those Merit devices and it came in the mail this weekend. I promptly ran to my shop to try it with my favorite rifle. I stuck it on my shooting glasses and thought it was a great improvement. But I felt it was a little wobbly and had a feeling that the suction cup would release and drop off at the most inconvenient time. I spoke with a guy at my club recently that had black electric tape with a hole in it on his glasses. Any I thought I'd try that. So I replaced the Merit with the tape. Just my opinion the Merit is overrated and overpriced. I think the tape with a 1/16" hole punched in it is perfect, maybe because it's closer to the eye. It doesn't move and I think the sight picture is much better than the Merit.
I'll probably keep the Merit but won't likely use it.
With all this being said, Black tape works great. Cheap, easy to make, very low tech, and a small roll of tape is a lifetime supply of optics for you and all your good shooting buddies.