There's nothing too remarkable about the first stage. Their second stage is what they're selling themselves on. There's no currently operational re-usable seco

There's nothing too remarkable about the first stage. Their second stage is what they're selling themselves on. There's no currently operational re-usable second stage. Starship is supposed to become a reusable second stage. Rocketlab's Neutron (their new rocket in development) only has a re-useable first stage. Their second stage uses an aerospike of sorts, letting their engine end also be their heat shield. This is different from what Starship is doing. Their heat shield is also cooled by propellant. Everyday Astronaut has a writeup and video: https://everydayastronaut.com/stoke-space/ https://everydayastronaut.com/stoke-space/ I think a lot of their viability comes down to how well their fuel cooling system works, and how broad of a range they can operate in. Every bit of fuel they need to carry for "cooling only" purposes (as opposed to also providing needed thrust) is $$$ lost.