I'm going by the article (pdf file) by Cristina Bramanti et al, "The Innovative Dual-Stage 4-Grid Ion Thruster Concept – Theory and Experimental Results," DS4G-IAC-06-C4.4, International Astronautical Federation, 2006. ACT-RPR-PRO-IAC2006-DS4G-C4.4.7.pdf
Tables 1 and 2 provide the performance and operating characteristics of the prototype DS4G device for the first and second testing campaigns in Nov 2005 and May 2006, respectively. In the first campaign, the best value of thrust is 2.85 mN; maximum values of beam power and RF power are given as 260 W and 490 W, respectively, and beam diameter is 2.3 cm. Table 2 provides a best value for thrust as 5.4 mN, maximum values for beam power and RF power as 398 W and 316 W, respectively, and a beam diameter of 2 cm.
The tables also shows improvements in efficiency in the second campaign compared to the first.
The Wikipedia statement ("A 4-grid ion thruster with only 0.2 m diameter is projected to absorb 250 kW power. With that energy input rate, the thruster could produce a thrust of 2.5
N.") is a projection of what someone would expect for the capability of a scaled up version. It is an unsubstantiated claim; no basis is provided in support of such a claim.
In the second table of the ESA article, the total energy (sum of beam and RF power) is 614 W, or 0.614 kW. The thrust of 0.0054 N (5.4 mN) divided by 0.614 kW gives 0.00879 mN/kW (or 8.79 N/MW). Assuming that ratio can be applied to 250 kW (i.e., the same efficiencies can be realized in the larger version), then the device could produce about 2.2 N of thrust. This requires scaling the beam diameter from 2 cm to 200 cm, which implies a commensurate increase in the grids.
I am not aware that a DS4G device with a 0.2 m (200 cm) diameter has been built and tested. it's not clear what that would look like.
I don't take published articles at face value as they are summaries. For application or utilization of data, I'd want to see the design details and test reports.
Note that in the Wikipedia article, the section "Experiments proposed and tests done," is empty. The article certainly does not provide a basis for scalability from the prototype to the large scale.
Consider thrust requirements for Galileo and Cassini spacecraft.
https://en.wikipedia.org/wiki/Galileo_(spacecraft)#Propulsion
To save on fuel and propulsion demands, the Galileo craft was sent from Earth to Venus and back passed Earth using gravity assist.
https://nssdc.gsfc.nasa.gov/planetary/galileo.html#overview
https://www.jpl.nasa.gov/news/galileo-heads-towards-second-gravity-assist
https://spaceflightnow.com/galileo/030920overview.html
https://articles.adsabs.harvard.edu//full/1997ESASP.398...53K/0000056.000.html
Cassini had a slightly more powerful propulsion system - "Main (445 Newton) engine for propulsive maneuvers" and 16 monopropellant hydrazine thrusters of which eight were prime and eight were backups.
https://solarsystem.nasa.gov/missions/cassini/engine/
Cassini was launched from Earth on 15 October 1997, "followed by gravity assist flybys of Venus (26 April 1998 and 21 June 1999), Earth (18 August 1999), and Jupiter (30 December 2000). Saturn arrival was on 1 July 2004."
https://solarsystem.nasa.gov/resources/11776/cassini-trajectory/
Getting a crewed spacecraft of many tons in short time, e.g., several weeks to a month, would require a substantial power plant and propulsion system. What would scaling from 2 N to 2 kN look like? From 250 kW to 250 MW?
The ESA paper has one comment, "Taken to the extreme, a human Mars mission using EP would require about 8-15 MW power and deliver a thrust of 90-180 N." That's more modest than 250 MW. On the other, the thust is fairly low 0.09-0.18 kN, and no basis is given for those thrust requirements. Taking the maximum values of 15 MW
e and 180 N, that gives 12 N/MW, which is greater than the 8.79 N/MW achieved by the prototype DS4G. One then has to devise a nuclear power plant to provide up to 15 MW
e, which might be a 50 MWt plant if an efficiency is 0.3.
The Kiwi NTR was tested at full power, 1 GW, briefly with a thrust of about 74,000 pounds, or 334 kN.
One can find some references on rocket vehicles here:
https://www.sciencedirect.com/topics/physics-and-astronomy/rocket-vehicles