Not open-source, but I trust them because I learned of it from some long-lost forums (which also had hacked printer firmwares to patch out such things), and others had also not experienced any problems. I trust the community far more than the manufacturers (who are certainly doing things against my interests), it reminds me of this:

https://news.ycombinator.com/item?id=13925994

I did sniff the communications it did with the printer, so I could probably write an open-source version if I really wanted to; but I don't think there's all that much value in doing so.

...but someone did think there was, so there's this: https://github.com/lion-simba/reink

Do you really have recourse against HP? I don't think they would have pulled this bait-and-switch if we did.

Well, in my case it's probably the difference between buying a printer or not, not buying HP or not. My wife has a printer (Epson) for her home business, and I'll have her print me something occasionally, but for a business I'm willing to make some allowances. For personal use, I've been so disgusted with the printer market for decades that removing those companies from all aspects except manufacturing and initial purchase is the only thing that makes that purchase palatable.

So, the question becomes, what's the cost of removing those companies and their supply chains/software after purchase? If it's well trusted software that doesn't require constant attention, that's attractive. If it's random people providing binaries in a country that I may or may not have any chance of getting recourse if they harm me (that is, trajan horse or exploit, not accidental hardware bricking/breakage), then I'm left wondering whether it's worth it.