I had one of those... It was a pain in the ass. The first long ride I used it I kept getting head aches, I thought it was because it was 90+ degrees outside, I later realized it was the insert. If you don't get it completly flush with the face shield it will cause it to have the effect of a cheap pair of reading glasses, not noticible at first, but eventually messing with your vision.
I thought I had mine flush against the face shield, and I may have, and it still caused problems. Like I said, I didn't notice on the short little trips back and forth to work, but after riding a few hundred miles only stopping for gas, it became a problem.
Also, when you clean it, follow directions, only use soapy water, anything else will screw it up, and soapy water doesn't work too well.
I hope it works better for you than it did for me.