I have no experience with that private mode. The creator says, he tried WordPress though:
> I tried using WordPress but it took too many custom plugins and configurations and I still got bombarded by spam signup requests.
> I tried using WordPress but it took too many custom plugins and configurations and I still got bombarded by spam signup requests.
One could reduce that amount of spam signup requests that one gets by simplying adding a captca such as recaptcha[0] or hcaptcha[1]
Dropbox is "just" a private s3 bucket with s3cmd on a cronjob -- or a million other technical solutions -- but they're a successful business because they nailed the user experience for average joes.
The point of OP's product is that you don't have to cobble together a bunch of hacks to replicate the desired user experience, it's supported out of the box.
For public signups it is a perfectly valid solution to use captcha!