I didn't build a Full Body Ultrasound but I know the people that did

Here's my take as a radiologist: this seems like a neat imaging tool that complements existing imaging tools (CT/MR) with new tradeoffs and questionable value. If whole-body ultrasound does provide value, it'll take quite a while (likely decades) for this to become a standard imaging tool offered by hospitals and physicians because the clinical trials to show any positive value take years, and then you have to convince insurance companies and Medicare to pay for it, and then you have to establish guidelines for physicians explaining when whole-body ultrasound may be appropriate to order.

Like the video says, this isn't a replacement for MRI or CT. Ultrasound has amazing superficial spatial resolution, but it falls off dramatically with depth, so the center of your body is essentially un-imageable. Ultrasound also struggles to penetrate air and bone. The video says having multiple probes around your entire body helps mitigate this, but I'm skeptical about how much that helps in practice. Your lungs take up the vast majority of your thoracic cavity, and your partially air-filled GI tract takes up a lot of your abdominopelvic cavity.

Based on how other preventative care and screening tools have panned out in recent years, I think this is going to yield pretty blurry images in relatively healthy patients that push them into getting more conventional imaging (e.g., MRI or CT). This in turn yields more false positives and biopsies with non-zero risk that likely outweighs any potential benefit of whole-body ultrasound. Counterintuitively, it's rare for proactive/preventative interventions in medicine to actually help people.