I agree... buy one if you are planning on more than one baby. And most are not very expensive. I think hiring costs about $50, and you can buy one from about $100.
I wouldn't of been without my capsule either, it is much easier with a little baby, and a newborn would seem soooo little for a carseat!!
I think most brands are very simialr, so it may come down to which buggy you have, if you want one that will fit into your buggy. I would reccomend one that has a base that straps into the car, it is a lot easier and quicker (esp in the rain etc)