I just finished adding SSO to the (very small) SaaS company that I work for, and this page gives me mixed feelings.

Yeah, SSO is a security feature and you expect to get security for free. But SSO is not free for us as the service provider. We pay a vendor (Auth0) a decent amount of money to handle all the hard stuff. We also have to manually set up SSO for each of our customers who want it, which can take anywhere between 10 minutes to several hours depending on whether the customer has set up SSO before. For these reasons, we charge an annual fee for SSO on top of the regular subscription fee. We're just not big enough to absorb the cost.