Weaknesses: A little noisy especially if you need to use it at night. Sounds like a mooing cow!
Overall: Really good and much easier to use than a manual pump. I had mastitis and found it really useful during that as I found it less painful to express on the infected side. Expensive but well worth the money.
Weaknesses: Noisy but think most breast pumps are.
Overall: I paid for mine with my Advantage Card Points at Boots. Better than manual pump I used to have which took ages to get any milk & my hand ached after using manual pump.