I tried it and I failed! Can't see s@#t but I guess need training. I definitely know it will be useful because as I was trying to focus on a very small spider (doing macro) I kept missing it as I couldn't see where it was through the lens. If only I can have both eyes open and spot it with my other eye.
hmm, kinda reminded me of my biology laboratory sessions in sec sch days, where we were trained to look through the monocular microscopes with both eyes open. imagine using only one eye for a few hours straight, tt'll be kinda tiring to achieve. haha.