Just as you probably already have,I GOOGLED the subject & the answers range from yes-no-maybe so & everything in-between.
General consensus seems to be having NFC turned on but in a non-use/stand-by mode uses very little power & only scans periodically while in this mode.
The activity that triggers NFC will use more power,but,this is almost always a short-term activity & power consumption should be negligible & return to a stand-by mode once the activity is complete.
FWIW,I discovered that the NFC "SWEET-SPOT" is located @ the top of the phone,near the camera lens/flash.This may help in placement of NFC tags.
Thanks for posting this! I've put up a couple of NFC tags and I've had some challenges with the phone recognizing when I'm tapping it and I'd have to tap in many different areas to catch it. The first time I did it at the top of the camera, on the "T" is what I call it, it recognized it instantly. Good stuff.

I just wanted to hear "oh no, that's bogus. The ring wouldn't cause any problems. Your phone is a dud, you should unroot/relock your phone and send it back blahblahblach" or "I think you may have fried your NFC chip by putting a dang magnet around it you pretty much ruined your phone way to go blahblahblah"