Looking for answers to these questions and references.

Avent bottle nipples and nipple shields are both silicone. What is the
difference between using a nipple shield (when one is indicated) and
using  an  Avent bottle.  Yes, with a nipple shield the mother may not
have to pump, so it is less time comsuming and then she dosen't have to
buy bottles, but anything else?

Has anyone seen or heard of Avent bottle nipples causing less nipple
confusion?  Are there any references for this?  Does the baby keep
their tongue down and  over the lower gumline better with an Avent
bottle than with a nipple shield, or is this the same as far as the tongue
position is concerned?

Thanks!  Your responses will help a lot!