I noticed in the FAQ you refer to your three secret types as text, redirect, and neogram. In other places you seem to call redirect "link". Could be a naming consistency fix.
Features like delete after N visits or by X date might be useful too.
I'm a little confused about the use case. Maybe I'm boring, but who would I need to send a scrt.link to? I can think of bad use cases, for example maybe a botnet could propagate messages through this, or share credentials that would change after using or something. I can't really think of other use cases though without going a bit unrealistic.
I read the FAQ about why I should use it. I'm not sure it's great for credentials because if they aren't continually going to be available through the link, the other party will need to copy them.
If I'm doing something with minor security concerns, e.g. sharing the Netflix password, I'm just going to send it over text or whatever. If it gets compromised I'll just reset and change it. If I'm doing something with significant security concerns, e.g. sharing credential to access a production database at work, then I'm obviously not going to use this due to trustworthiness concerns.