Open marriage only works for certain couples. Not all open marriages are swingers, some are poly. If the relationship is just for sexual gratification outside the marriage, then it's swinger. If it's for a secondary relationship that honors the marriage as the primary, it's poly.
If you are a jealous person, open marriage is not for you.
Now if you can manage your jealously, and understand that it's a learnt trait, not actually a normal human reaction, you might just be able to handle an open marriage.
Jenny Block just wrote a super book that even a monogamous members of marriage should read just because it will make you smarter about how your perceive what marriage is, and how people over the years have contorted it a bit, thanks to the media particularly in the last 80 years.
The big thing above all, is having a honest open marriage. Where both really talk about it to all kinds of details, and they actively work to manage it. It's harder to work in, than say a monogamous marriage, but it can also be more rewarding if done right. It's not without it's risk either. I would define it as a more evolved marriage, not something for the faint of heart, or for a young marriage with people who are lacking in real education.
Oddly, I would say that a couple should not strive to be open, but arrive at it one day when the sex slows down. It spices it up, if done right.