Have you seen the privacy policy for this service? Clearly not GDPR compatible. Simply using this means you cannot service the EU. Also, if your issue is that

Have you seen the privacy policy for this service? Clearly not GDPR compatible. Simply using this means you cannot service the EU. Also, if your issue is that owning your user passwords is difficult, then I'm sorry that's just the nature of the problem. It doesn't get any easier by offloading the problem to a third party. Bcrypting passwords is not rocket science anyway. MFA libraries exist for pretty much any server library you use. Sure a company dedicated to doing user management will definitely do a better job than you, but only if your needs align with those of the majority of its users. The minute you want something custom,and trust me you will you're back to doing user management yourself. Only now you have a giant opaque blackbox to deal with. Also, tomorrow if Google buys the company,I'll have 20 hours of notice to integrate my own user management before they shut it down. If Facebook buys it, they'll use my user data for targeting their advertising. Either way, I'm in deep trouble (If I care about my users, which I think most people will). Even ignoring these, the simple fact is that by the very nature of the company, it is a much bigger target for people trying to break into and steal user information,than my little saas could ever be. I'd wager for most people using such services they'd be more likely to get hacked as collateral damage rather than being targeted.