I just thought I would share my story, I thought it might be helpful. I had a Playtex pump and it was great, except the motor is not very high quality and it died and then the replacement they sent me did the same. So I gave up on that and got a Medela, but the breast shields are terrible on the Medela and it didn't work for me.
So I used the playtex tubing and shields with the Medela motor and it is the BEST! I had to ship the whole playtex setup back to Playtex to get the refund, but I went on the playtexstore.com website and bought another set of their tubing and breast shields, so everything works now.
Anyway, if you are having trouble with milk production with a Medela pump, that is my recommendation - try putting the Playtex shields on it. They are great. But I don't recommend using the Playtex motor. It stinks.