Do you need them? I believe you do. Writing is a business. Therefor you do need them.
Make them yourself or order them? I've done both but I really prefer making them myself. I use both sides which costs more if you order them that way. Plus I can do as many as I want or as little for the cost of the ink and business card stock which are pre-cut. Depending on where you order them, the quality will be different. And then you are limited with what you can do for the price. When you make them yourself, the sky is the limit. I like putting a pic of me on the front with my information and then the covers on the back.
What information do you need?
Your pen name
Website (yes, you need one)
Book Title(s), price, ISBN #
Space is limited so choose what you want on the card but do remember you have both sides to use if making them yourself or ordering them. Just check the prices and go with what your budget can afford.
And once you get them, never pass a chance to pass them out lol. If you get people to your website, they have a 50% chance of buying your books. That's more if they never hear of your books at all!