[compass_copium]

>However, there is some light evidence that the variation I see is not just intra-day variation. Specifically, there are several species that stay consistent in frequency across all samples: e.g., Neisseria subflava, Streptococcus viridans, Streptococcus oralis.

Disagree. You can not make that claim without sequencing your mouth's microbiome in the absence of probiotics for a month as well (and, really, many more than one persom's). Was your diet controlled all month? Oral hygiene habits? Any of a million other variables?

Also, it's worth pointing out that the study was designed to test one hypothesis, and you need to be very careful about looking at further claims. This test only really provided evidence that these probiotics don't introduce L. reuterii.

[Aurornis]

Unfortunately self-testing something like this isn’t trivially cheap, so the self experimenters tend to skip the very important control step.

This happens a lot when people discover that you can order your own bloodwork. Reddit supplement and biohacking forums gets a lot of posts from people sharing bloodwork from two different dates and concluding that the changes are entirely due to their supplement regimen. When you’re only getting a couple tests it’s not easy to see that even day to day variations in these tests can be very large. Even timing of tests during the day, how you slept, or what you ate can have a lot of impact on many tests.

Doing some basic controlling without taking the supplement is important. Doing double-blind tests on yourself also isn’t that hard if you put some effort in. There have been some surprising results from people doing controlled tests on themselves and discovering that the supplements that looked promising on paper were either doing nothing or were trending toward being negative. Gwern’s experiments with magnesium supplementation which were generally flat with hints of trending toward being negative are a good example. That experiment was a good reality check during the era when the popular narrative that we were all severely magnesium deficient and the solution was high doses of magnesium for everyone.

[rossdavidh]

Well, they did say "light evidence" rather than "proof".