So you're saying you trust a single developer to both write an encryption tool and run the servers it talks to more than the combined possibilities using existing open source tools to create backups by encrypting data locally and storing it remotely via ssh/sftp?
Yes, when it comes to crypto I'd put my in trust in highly talented people over trusting my own ability to glue together a collection of OSS tools anyday.
I didn't suggest you should write your own encryption tool. There are numerous open source tools for creating encrypted backups, some do deduplication first too.
If the tool doesn't happen to support remote storage, a simple rsync or scp fills that part.
Literally the only thing unique about this service is the use of the term picodollars and the single individual it's all reliant on.
When Drew first do a "Show HN" [0] (before it was a thing, actually), there were a lot of response about how it doesn't do anything new that couldn't be already done by a technical inclined person (see the first two top comments in the posts).
To make a comparison with tarsnap, while it's probably possible to do encrypted backup manually with a combination of shellscript and such, there are just too many moving pieces that can go wrong. Where do you store the backup? Someone mentions S3, but even managing backup on S3 with deduplication is not something trivial, and managing the encryption process is definitely not something most of us can say with confident we won't mess up. I can imagine a thousand way that I encrypt something, then unable to decrypt it back.
And then maintenance is also an issue, if I'm using a set of OSS tools, I would have to make sure the tool is being maintained, and to follow any potential disclosure on bug/ updates etc. With Tarsnap, I know I will get an email from cperciva if something comes up.