One thing the article neglects to mention is, importance of temperature for ongi to work effectively.
The lactic acid bacteria produced during kimchi fermentation is most active right around freezing temperature, so ongi needs to be buried underground in mid December.
The bacteria are definitely not more active near freezing compared to a warm room, ferments happen much quicker when it's warm.
I have no doubt that you can make superior kimchi in ongi, but only if you're an expert. Regular folks would get better and more consistent result sticking with 'ongi' powered by electricity ;-D
They're really versatile. The oversized compartments are perfect for storing a large amount of galbi, watermelons, beer, etc. especially since you can set different temperatures for each compartment. I don't know anyone who uses one exclusively for kimchi anymore.
In the past, people made a huge amount of kimchi in the fall when cabbages are cheap, and expected it to last until the next year's first harvest of fresh vegetables. The near-freezing temperature ensures that the kimchi remains good for up to 6 months. Some kimchi can be aged for 3 years or more. So of course the preservation method is focused on stopping almost all microbial activity, including that of lactic acid bacteria. The goal is to maintain a sort of equilibrium for as long as possible. The onggi probably also helps with that.
Nowadays, many people in Korea buy pre-fermented kimchi instead of making their own. Several national brands and dozens of independent sellers with wildly different styles can all deliver kimchi to your door. In that case, you either set the fridge to preservation mode immediately, or keep it warm for another day or two if you prefer to ferment it a little more.