I have a client who has twins (I previously posted about these babies; they
had lots of bottles, but were easily transitioned to breast once strong
enough.)  One baby has colostomy bag and has just left for the East Coast to
undergo surgery for bowel blockage.  Mother was sold a PNS by someone at
the hospt. where she delivered. I personally do not sell the PNS, preferring
in a clinical practice to only deal in clinical grade pumps.  It was
presented to her as a clinical grade pump.  She had (as you may recall) very
sore nipples as a result of nipple candida.  This was successfully treated,
however nipples remained very, very sore.  I checked positioning and did not
observe nipple distortion, nor detect any odd oral anatomy or function which
would suggest sucking issues.  Besides, due to the soreness, mother was only
putting babies to breast once or twice a day.  She was pumping like crazy
with her PNS.  She called in despair, wanting to keep at least the ill twin
on human milk through his surgery. I had already suggested lubricating pump
flange.  I had her come in and pumped her on both the classic and the
lactina.  Niether hurt.  I sent her home with a lactina because it is
lighter weight and she can travel with it.  She worked with it for a week
before leaving for NY and her nipples were vastly improved.  I think that
the diaphragm release is slower than the piston release, sustaining the
negative pressure for slightly longer.  Some women (working moms) have told
me they like the sensation of slightly stronger suction.  It may be
inappropriate for women who have had nipple problems.
Barbara