I'd suggest making it very clear in your docs whose data you're managing, and (assuming it's all the customer's and you don't lay claims to it) how would portability work. I wouldn't want to use this without a very clear understanding of what I'm locking my customer base into.

Are you offering any security benefits?

What security is there against malicious insider threat? (Eg can you / people at Clerk impersonate any of my customers on demand? Is there auditing/accountability for such activity?

Is this something that sites with crappy roll-your-own user management would be advised to migrate towards, and if so why?