In UK we use these almost routinely.  They are made by Egnell.  Those of us who
hire out Egnell pumps (the electric automatics) have recommended them for some
time, and they are standard now in the accessory set.  I don't know of research
to support their use, though there may well be some.  We feel (and mothers
report) that they are more gentle - the action is a combination of breast pulled
into shell and silicone insert pulled in and out against breast.  This also we
believe gives better stimulation, and would be particularly helpful for a long
term pumping for a prem.

At the very least, I don't think they do any harm!

Mary Broadfoot, Paisley, Scotland
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Just home from a study day in London!