The original study [1] uses Vivomixx in about double dose.

According to them it's because it is easily accessible and has multiple strains of bacteria in it (they were not trying to go for one strain in particular).

1 : chapter "Study intervention" of https://www.nature.com/articles/s41398-022-01977-z

I don't know much this topic, but if you are looking for supplements make sure they are refrigerated. Yogurt is probably the easiest/best way to ingest them though instead of specific pills.