Need? No. But I guarantee you'll use it.
My wife used to do it manually. The electric pumps were pretty pricey, but in the haul it was really worth it. Pump breaks at work got down to ~:20. Additionally, she spent a while trying to build some kinda rack so that she could do it hands free. eventually she settled on zipper-cup bras. After getting everything situated, she'd just zip the thing far enough to hold the suckers in place and voila, reading time!
Extra credit answer:
Get an ice bucket that you'd use for holding "manual" ice... not sure what it's really called, but when you have ice trays, it's the rectangular bucket you dump the ice in. That thing is the perfect width for the "Lact Packets" as we called them. Lay them flat to freeze, an hour later stand them up in the bucket. New in rear, pull from front.
Once we had it organized like that it didn't really matter how many days we had because it all took up the same amount of space. I think at the height of the "what the hell do we have all this milk for?" time, we probably had upwards of a wk in that bucket. Just store whatever you're comfy with.
Extra extra credit info:
Storage times. . . In the regular freezer, 2 weeks. In the deep freezer, 2 months.
 Just talked to the wife, she said that you'll get a 'fuller expression' with an electric one, which IMO pretty much settles it. More per sitting in less time.