"But it’s still a closed, proprietary database and there’s no way to decode an “Oh By Code” if the service goes down, which is the disadvantage number one you have with URL shorteners."

Yes, that's correct. In this case, "Oh By" will continue running indefinitely. This is true for two reasons:

1) Building an extremely lightweight, ad free interface has a happy byproduct of ... being extremely lightweight. The infrastructure requirements for even a wildly popular "Oh By" are trivial.

2) Because Oh By is self-funded, there is no pressure from outside parties to break the pattern of an ad free, tracking free service with zero bloat.

If you're having trouble swallowing this, remember that rsync.net has been running continuously since 2001[1]. I think that's a credible track record[2].

[1] As a feature of JohnCompanies, the first VPS provider, and then as a standalone corporation in 2006.

[2] In fact, the rsync.net warrant canary turns 10 years old this year.

"How do you plan to get people to know your service if it’s not recognizable? Let’s say I put one of those codes on my business card, I still have to write somewhere that people should use 0x.co to access the content, which ruins the advantage of having just one code rather than a URL to my website (literally anyone knows how to open a URL in a browser)."

Well that's the real trick, isn't it ?

I'm happy to report that while Oh By itself does not display ads, we are a consumer of ads. We have a decent budget for sales and marketing.