A string loop will help make a small correction on a peep's rotation, but it won't flip one around 90 degrees. You've got to adjust the peep so it comes back to your eye correctly with no help. It's a pain in the rear to do but well worth the effort. Then the loop will be a little insurance.

I've got a 1/4" G5 that I tried out on one of my bows. It worked fine, but I went to shooting barebow. I'm about ready to set up a bow with sights again, so it's coming out of retirement.