I gave up pretty fast on the e-mail option since I had to set up a mail server and it was painful... we use Google for e-mail and it could not use that, and setting up anything else is a many-step time sink.
I did not want sandcats.io but to use this on a private (ZeroTier) intranet. Even for your enterprise offering, which we might be willing to pay for, you still don't have a clear and simple way to auth. For enterprise I have to set up LDAP or other complicated nasty things.
My personal rule for UX:
Each step that must be performed to set something up cuts the adoption rate in half. So if you have an audience of 1000 and 4 steps, 63 people will end up trying your product.
That's not hard science, just a rule of thumb I use to impress upon myself and my team how important UX and zero-config is. It does have some basis in logic. Think of each step as a bit in an integer for 'cognitive load.' Each additional bit increases cognitive load exponentially, not linearly, since the total setup involves the specification by the user of N bits of information.