Cliffnote version is: stellarators are hard/expensive to build. The test run shows this one seems to be built correctly.
Simplifying a ton one could compare the two competing designs as follows:
stellerator: harder to build, easier to run (and more efficient)
tokamak: easier to build, harder to run (and less efficient)
Due to the first property, there are more tokamaks around and showing basic functionality for any stellerator is a good/important step.
Edit (relevant quote from the article):
"""Although there are about a dozen stellarator experiments around the world, including in the U.S., Japan, Australia and Europe, scientists say the Greifswald device is the first to match the performance of tokamaks."""
stellerator: harder to build, easier to run (and more efficient)
tokamak: easier to build, harder to run (and less efficient)
Due to the first property, there are more tokamaks around and showing basic functionality for any stellerator is a good/important step.
Edit (relevant quote from the article): """Although there are about a dozen stellarator experiments around the world, including in the U.S., Japan, Australia and Europe, scientists say the Greifswald device is the first to match the performance of tokamaks."""