Nipple shields I believe are really for babies who are unable to latch on properly. Some people use them for cracked or sore nipples, but sometimes they are hard to get off of for babies so I wouldn't use them unless I had to.
I had a preemie and HAD to use a nipple shield. I would never use it unless I absolutely had to. Took 10 weeks to get off that *#$*@# piece of silicone. I wanted to burn all of them once we finally shook them, but we had to go back to them again later because he wouldn't nurse without them again. Would never use unless I had to, ever!
The Lansinoh lanolin stuff was okay, but I used it for like, 2, 3 days maybe? I was pumping exclusively at the time to bring in supply though. When LO started nursing without the shields my nipples got more bruised feeling than cracked and bleeding. I used the Lansinoh soothies gel stuff, THOSE were the bomb!