"Open hardware" phones tend to be overpriced, gutless, and clunky compared vs mainstream branded phones. They can't leverage any of the economies of scale which define the consumer electronics manufacturing, logistics, and licensing industries - they can only afford (expect to sell) small production runs at the worst cost rates. They can't afford substantial in-house development of new tech.
You're really paying for "environmental sustainability". The phone is made with methods and materials which minimize environmental impact. The phone can be recycled and reused. The phone is energy-efficient, both in usage and in charging. Unfortunately, a lot of this is greenwash - if giants like Apple can lie about it then little kickstarts and indies who aren't as closely scrutinized can get away with it, too.
And you're really paying for DIY support, for Right-to-Repair, etc. I'm all about this stuff! But I admit it's niche, it's not really the best choice for everyone. As far as repair and reusability promises - the ability to easily add or replace or upgrade modules, to configure the hardware any way you like, to extend the life of the device indefinitely - remember that lifetime promises can't be kept when small startups don't survive.
This Teracube looks promising. But so did Fairphone, which is still producing expensive mediocre devices. And so did Shiftphone, which is even more expensive and even more mediocre. And so did Neva, Andro-One, Delta, AltPrime, Ultimium, many others - ambitious over-their-head startups which all turned into vapor (and which have all magically vanished without a trace from public domain or public record).
