We get this question all the time and no, it's not worth it for a small business or an SEO working for a small business to use Yext. The cost over the long run compounds vs manual building and if you cancel, you lose your listings.
Over 5 years you'll have paid Yext ~$2,500. In 5 years you'll still have only paid the fee initially if you build manually. With us that's a savings of close to $2,000. It just doesn't add up.
The only situation I can think of is maybe with a client that updates their hours constantly and just doesn't listen to you when you say that updating your listings on a monthly basis is unnecessary. You know, the client that wants to update their pictures once a month and has bought the incorrect assumption that "fresh" information on your listings will help you rank higher. Get Yext just to make the client feel better in that case.
I'll also echo what others have said about enterprise. It is a solution if you're managing hundreds or thousands of listings.
Beyond those two use cases, and for 99% of small businesses, go with manual over Yext.
P.S. In the interest of full disclosure, I am the President of a company that runs a manual citation service. So while I think my opinion is unbiased, I'll let you decide
