I have an Ameda Purely Yours Double Pump that is 4 years old (still working fine). My sister is due with her first in September and she asked what kind of pump I use and registered for the Ameda they had at BRU. We have decided to get this for her as a gift, but I see there they now have the pump I have (which is drastically cheaper) and then a new one that is and "Ultra" pump. What is the difference between the two pumps?