I say definitely buy this after baby is born.

Even if you do b/feed successfully - you might not use it. I sent Dh out to buy mine when DD was maybe a week old because I had cracked nipples and couldn't feed. But once my nipples healed, I never EVER used it again - and I breastfed until 12 months. A breast pump isn't essential to successful breastfeeding. Plus, my hospital and later my community health clinic both loaned me their electric pumps when I was having problems.

They are pretty readily available from almost any chemist - especially the Avent one so I always say wait and buy it if and when you need it...