I don't have to send big files all that often, but I love the idea of using a service built around encryption and privacy, that will also auto-delete or expire using the settings I provide. That seems a lot safer and cleaner than dropping it into a Google Drive or Dropbox account and then sharing access to that folder forever. The fact that it's open-source and built by Mozilla is of course also a huge positive.
This isn't a common need in my life, but I'll be excited to give it a try soon.
It's more an alternative to wetransfer.com/ and friends than Dropbox or Drive. But for sharing files on those services I've had good success encrypting files myself and then sharing the key via a side-channel. Slightly less convenient, but works well enough.
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