It may still be better than nothing, since they didn't test nothing. Citric acid was better than vinegar for them, but still showed worse yield than phosphoric. I tried citric acid myself and found that its pH down effect disappeared within hours, as some combination of the plant itself and the root zone microbiota broke down the citrate:
The professionals generally use mineral acids, and I believe that's with good reason. Of those phosphoric is the safest to handle, though a significant corrosive hazard in concentrated form; carefully dilute to ~2% for day to day use. You could also try monopotassium phosphate, but if your water is hard then you'd need such massive amounts that the extra K and P may become problematic.
Where do your get all this info from? This shit is fantastic. I’ve been scouring the wasteland of the internet for decent plant knowledge and seem to go from oasis to oasis in a vast desert of seo garbage
It's helpful to learn and use professional terminology, to get away from heavily SEO'd search terms. A search for "when to water potted plant" returns endless variations of the same mediocre article, but "coir irrigation frequency" returns good stuff.
You can use citric or phosphoric acid though.