This is not a "breakthrough", it's an announcement that they turned their machine on for the first time and took the first measurements, and measured a signal (i.e. reaction rate) so small that they have to go through some lengths in the paper to convince the reader it actually represents the reaction in question.
This is certainly progress, a genuine accomplishment, and a necessary step along the way to their ultimate goal, but it's a bit of obnoxious puffery to call it a breakthrough, and I don't think it resolves any of the fundamental questions about whether this reaction (which is something like 100x harder than the typical DT fusion reaction) will lead to a viable system in our lifetimes.
Yeah, the fundamental physics constraints of this approach are pretty wild. The cross section peak for the candidate Proton-Boron interaction is at about 10 times higher energy (i.e. temperature) and the peak itself is roughly a fifth of the Deuterium-Tritium cross section. Oh and each individual interaction produces less than half the energy. So 100x more difficult is actually not far off in that sense. That means you don't just need a lot more energy to sustain the reaction, you'll also get a lot less energy from it. This is a very long and steep road to net energy production and there are good reasons why noone has bothered with it so far. The only upside is that you produce more charged particles, which are easier to control and extract energy from and they also cause less radiation damage. But if anyone ever makes a reaction like this work, by bet is still on Helium-3. But we won't be able to make use of that until we have scalable mining industry on the moon's surface.
Helium-3 can be made on earth by fusing deuterium nuclei. Which is a lot easier than fusing Helium-3 nuclei, so if you can do the latter the former is probably a lot easier than going to the moon.
If it was easy to create Helium-3 via fusion we wouldn't need it in the first place. The whole idea is that He-3 fusion might be easier to harness because it produces fewer neutrons. And if we can't create it as byproduct in a net energy gain scenario this approach is only useful for spaceship fuel at best.
I guess, hypothetically, you could have giant D-D power plants producing He3 as a byproduct, which can then be used in smaller more portable applications like (space)ships.
The whole point of H-B11 fusion research is finding ways around the naive interaction dynamics in order to take advantage of superior aspects.
Instead of being open to the possibility of such ways to exist, the physics community appears to prefer to bend over backwards in their efforts to disparage even the mere idea of alternatives to mainstream approaches. When did they lose their appetite for revolutionary ideas?
This is certainly progress, a genuine accomplishment, and a necessary step along the way to their ultimate goal, but it's a bit of obnoxious puffery to call it a breakthrough, and I don't think it resolves any of the fundamental questions about whether this reaction (which is something like 100x harder than the typical DT fusion reaction) will lead to a viable system in our lifetimes.