With a deflection-sensing (conventional) stick, it takes a certain time to move the stick. If you're trying to do quick manoeuvres going from (say) full nose-up to full nose-down deflection, that fraction of a second can be a significant delay, especially in a fly-by-wire aircraft with powerful, fast-acting actuators. With a force-sensing stick, that delay is removed. Force-sensing sticks also cause less arm fatigue.
Others have pointed out that force-sensing sticks are also mechanically simpler, because of the lack of moving parts. This seems like a small concern, but for military aircraft, which get more frequent inspections and have a very stretched-out supply chain, removing any need for a replacement part can be a big benefit. It's the kind of design criterion where, even if it isn't really a huge factor on this aircraft, an engineer who was burned by a spares or inspection problem on a previous design might consider that a big project risk.
The mechanical simplicity can also make the extra buttons etc. on the stick more reliable, because there doesn't need to be wiring through a rotating joint, which might get trapped or wear insulation. And the fact you don't need space for the stick to move can make it easier to design other components around the stick.
As this project found, the chief downside is that force-sensing sticks are unfamiliar to most pilots, and they take a lot of getting used to. They also make training harder: with a deflection-sensing stick, it's easy to show a student pilot the appropriate stick position for a particular manoeuvre (e.g. to show the progressive pulling back in the flare). This is much harder with a force-sensing stick. Obviously, pilots won't be doing their initial training on this aircraft, but they still need to demonstrate handling characteristics etc. when familiarising on type.