I don't know how it feels to have rings on my nipples, but I can tell you how they feel in my mouth: not good! I don't ever place jewelry in my mouth, but I do love putting nipples in there! My vote would be no if you were my gf. Just my two cents.
Do they make clamp-on nipple jewelry? (I know they make clamps!) Maybe you could try them out that way to see what they felt like, or even experiment directly with the clamps to see how you responded to them. That way, you won't have done anything irreversible.
I can say that an ex-gf of mine had piercings done before I knew her. By the time I met her, she didn't wear them at all anymore, and the holes were closed. However, she said that it dulled her sensitivity on one side and she regretted that.