When comes to lower part it’s always bipedal (hard to balance) or wheels (low capabilities).
Why no one makes 4-6 legs, insect like?
That seems like an easier problem to solve while gives much better mobility.
Especially because this thing is already $8k, I imagine they have already done some substantial price optimization.
With three legs, as soon as you pick one up you will start to fall over, so you either need legs with enough freedom of movement to shift the center of mass of the robot back to offset the lack of support, or some other way to shift the center of mass.
You have to balance with two legs, as well, but there isn't a transition from "stable" to "balancing" with every step - you're always actively balancing - which makes movement easier to plan.
Overall I suspect that tripedal locomotion isn't really any more efficient than bipedal movement, and it might even be less stable.
Just one example: https://spectrum.ieee.org/martian-inspired-tripod-walking-ro...