Testing of propellantless propulsion concepts
requires a highly sophisticated thrust balance that
must be able to reliably detect very small thrust with
a resolution down to the nano-Newton range, block
electromagnetic interactions as much as possible
and limit any balance-vacuum chamber wall
interactions.
The thrust, if any, is so weak it's down in the noise. For a propulsion system, that's a big problem. It's like cold fusion in that way.
Nano-Newtons. For comparison, the tiny rockets used for attitude control on satellites have a thrust of about four Newtons. Falcon 9 booster, about 7,000,000 Newtons. This thing, if it works, maybe 0.00000001 Newton.
The thrust, if any, is so weak it's down in the noise. For a propulsion system, that's a big problem. It's like cold fusion in that way.