When i was pg with my first i bought a Tommee Tippee closer to nature manual pump, i used it as soon as i got home from hospital as my supply was in over load and i needed to take some off before DS could latch on and i found having the pump for this rather than hand expressing helped draw the nipple out as well. I continued to use the manual pump until DS was about 10 months old and then it broke, i definately got my monies worth though! ( i had used it heaps for expressing when i was doing night work and when i went back to work) ,I then bought a Medela Mini Electric, which is great and much faster than the manual pump.

Having the pump on hand as soon as i got home was great as it saved having to worry about getting access to one if i needed it ( we live out of town). If you're only planning to express occasionally then a manual pump should be fine, it does take longer but if you're not going to be doing it all the time it wouldn't matter. It really is up to you, they aren't essential but certainly come in handy. Good luck