I'm a satisfied owner of a PrimaLuna power amp, and am a fan of the brand.
However, I feel the hardwired super tube clock is a bit of a gaffe on their part being it's a consumable. Even if this tube lasts 10 years, who's to say you'll be able to obtain a replacement at that time? Resale is going to be a PITA since prospective buyers are going to want a definitive answer on age and hours of use.
They'd probably sell double the amount of these DACs if they wired those tubes to a socket and included a spare in the box.