I dont know what IMA insurance is, but I know with my insurance the brand does matter, only where you buy it matters. You can't buy it from a normal store like babies r us, walmart etc....you have to buy it from a Durable Medical Supplier. Also my insurance doesn't cover it unless its bought after the baby is born.
I had to call my insurance company to get a list of the companies that they will let me buy it from. This is the one they recommended. http://www.byramhealthcare.com/breastpumps/index.php The comapny bills directly to your insurance company. They have the Medela brand pumps which is what I would get if I were to choose my own brand anyways.