I was skeptical as to how such oscillations could have such an impact on trajectory given what I've witnessed with experimental and HPR hybrids over the years, but my scepticism has waned a bit since then.
Yes the matter moves from non-trival when many hundreds of liters LOX starts sloshing, and pockets a LOX vapour start forming in the feed lines & hammering.
I had a more detailed look over their site last night & watched the 18min speech the fella gave. I cant help but feel their key design rational are floored; for example the reasoning on the small diameter springs primarily from limiting themselves to a single cylindrical section, rolled from the largest alloy sheet they can source. Also that everything has to be shop weldable thus limiting them to metals, when many composites can be shop fabricated to a high standard these days. Also the same old concept that LOX is good because its cheap & available, without looking into the technical issues that complicate its successful operation. Or paying attention to the huge volume of historical failures at yeilding functional large propulsion systems based LOX by anyone other than multi-million dollar aero firms, is kinda silly in my books.
If I was going to take a crack at such a project I would be looking at storable propellant first off, most likely Peroxide. This would allow you to commercially source a very large & lightweight composite tank for low cost. As well as the use of COTS pluming and valve systems, so no more frozen ball valves. I wonder if these guys considered the difficulties of stopping ice build up while pumping LOX on an ocean based platform?. The Peroxide gives you excellent density, and pre-combustion with a cat pack; thus you avoid the combustion instability issues of LOX systems. Sure you have to clean everything and passivate metals, but you have to clean for LOX anyway and spills of either will kill you period. The arguments about the dangers of respective oxidisers become mute when you read the MSDS for any of them, as all can kill you in the quantities & application at hand.
I would then look at building a light weight external airframe skin (thin alloy sheet or composite) with an internal stringer structure (ie aircraft type structure), which could open your diameter up past 1.5m range. The vehicle would need active roll control and verticle stabilisation, but this could be achieved with a low grade vertical gyro & differential GPS.
A design with a central hybrid motor, surrounded by 4 vectoring mono-propellant chambers would give you viable steering.
Who wants make one