I’ve given both kefir and kombucha a go. There’s a lot talked about their benefits, but really they are only dramatically effective if you already have a compromised gut biome (which I do).
My kefir always came out far too grainy, and wasn’t the most pleasant to drink, but did wonders for my digestive health. I got out of the habit though – it’s a bit of a faff.
I had been drinking supermarket Kombucha for much of last year, with similar benefits, but it gets a little expensive. I have recently got a continuous brewing kombucha setup going, and it’s far more palatable, although the scoby looks, frankly, terrifying. It’s an easier and, happily, cleaner process than kefir.
I’ve only been drinking the home-brewed stuff for a week or two, and have found myself sneezing a lot (Some people call that a healing crisis or even a Herxheimer reaction, but internet health commentators are full of misinformation and misguided confidence.).
Some people also claim that the home-brewed versions tend to have a more diverse set of bacteria than the shop-bought versions. Can’t verify if that’s true.