1. It is, purely, bomb research dressed up as civilian activity for funding purposes. Everyone working on it has top-secret clearance.
2. It has no consequence for any civilian project. The target that produced a couple of MJ cost $10M. (2.4 MJ is <0.7 kWh.) A real plant would need to feed them in at a high rate. Q is not the important measure. Dollars out / dollars in is the right measure, and everyone is still at exactly zero, with no plausible prospect of ever exceeding 1.
3. Extracting useful energy would require capturing hot neutrons in a "blanket", heating it up, and running fluid through it to boil water to drive a steam turbine. The minimum practical size for such a "blanket" exceeds that of a large fission plant. To collect enough neutrons to be useful requires a huge volume of plasma, as even compressed plasma is very diffuse vs. fissiles.
4. Compressing the plasma with superconducting magnets could increase density, but then the neutron flux through the smaller surface area of the chamber wall would destroy it that much more quickly.
5. The hot neutron flux would also quickly weaken the structural parts required to contain the enormous forces exerted by the electromagnetic coils. Superconducting coils would impose even larger stresses. No research has gone into identifying a viable material, in decades, despite that none is known. After a short time the reactor parts would all become weak and (also) fiercely radioactive. Repairs would need robots not yet designed.
6. Civil fusion would require a large amount of tritium, which no one knows how to make economically.
7. Steam turbines cost a lot to operate, regardless of heat source. No other generation method relying on such steam turbines -- coal, fission, geo -- is today competitive vs. renewables. As the cost of renewables continues on down, they get less competitive by the day.
Fusion is intrinsically interesting, just not for power generation.
One company, Helion, is trying to make a fusion device that does not emit many hot neutrons. However, achieving conditions for this process, D-3He, is even harder than for D-T fusion. They hope to breed their own tritium, which would eventually decay to the 3He they actually need, but it is not clear how they will produce enough. (Fun fact, 3He loves to turn back into tritium.)
If they cannot, but they do get it working, it might end up usable for outer solar system exploration, which is difficult to power.
This "milestone" provides exactly zero meaningful information for the magnetic confinement fusion that is the only avenue being pursued for civil power.
Fusion offers no prospect of "unlimited free energy". It offers instead very expensive energy, or possibly none at all. We already have access to unlimited free energy, and need only build out the solar, wind, and maybe tidal systems to collect some as it goes by.
