Don't buy probiotics - eat quality grass-fed organic yogurt (such as Trimona [0]) and home-made sauerkraut - these have centuries of evidence. As a Bulgaria, we traditional make sauerkraut every year. It's pretty easy to have it, you just need a little more attention to it in the first weeks. The juice is amazing, too. You can buy it from Amazon [1].
Longevity in general (don't judge by today's fully Lidl-ized & Kaufland-ized diet of modern Bulgarians). The research dates back to the 19th century and Ilya Ilyich Mechnikov [0].
That's the issue with nutrition - you can't really randomize as every person is on a different diet that's hard to control. Plus, how are you going to radomize when people know what they're eating - you can't create non-yogurt that's identical to yogurt for the controls!
Well, you can’t blind it but you can still randomize. If your outcome variables are sufficiently objective and important (e.g., mortality or cancer risk, not just perceived health), the possibility that the causality flows through a placebo effect is much less worrying. If [people correctly believing that they ate yogurt] reduces [the incidence of cancer], great!
So you admit that those links you posted don't constitute evidence towards the products you suggested. Interestingly enough, you were so happy to dismiss the studies about probiotics yet you are so keen not to do the same for yours even when none of them have any evidence towards its benefits
[0]: https://trimonafoods.com/
[1]: https://amzn.to/3ZO0Sxl