Re: Interesting but....????
The fuel tanks are big structural parts of the rocket. Removing them saves mass.
Most modern rockets have 2 or 3 "stages". The reason they do that, is that the weight of the empty tanks is so high. At some point, it becomes better to get rid of the empty tanks, even if that means you have to carry an extra rocket engine up to power the second stage.
If you could get rid of the fuel tanks the way this rocket does, that potentially makes single stage to orbit rockets possible. That reduces costs because you only need one set of engines, not two or three. It also gets rid of the complexity of the staging manoeuvre(s).
Although there are other reasons you might want to stage anyway. In particular, the optimum nozzle design is different depending on the air pressure, so existing designs optimise the first stage engines for use in the atmosphere, and optimise the second stage engines for use in vacuum. But perhaps they can use a design that is good enough in both atmosphere and vacuum.
Note that this is only really better than Falcon 9 if they can make the whole rocket returnable and reusable. Otherwise, Falcon 9 is throwing away a second stage, and this would be throwing away the only stage, so it's not going to be competitive.