So far, this is the only artificial nipple DS has taken, but DH says it works great and is a great nipple for a breastfed baby since the baby has to actually suck to get the milk out and it doesn't just fall into his mouth. We've used it only a few times so far, but had no confusion those times switching back and forth. If that changes, I will update.
So, we would recommend the nipple, the only down side is the price. Its $15 for just the nipple!

and I'm not sure how long they are good for before they need to be replaced. I'm typically gone for 14 hours a day when I work (3 12 hour shifts a week), so we would only get a day's worth of nipples, and wash and reuse, but would we need to replace the nipple every 3-4 mo or no? Something I wish Medela would put on the packaging...