I keep kefir, both the dairy kefir and the water kefir.
I prefer the dairy kefir for ingesting, and the water kefir for topilogical applications. I just can't get past the smell and sour taste of the water kefir to drink it. It reminds me of beer or wine, and I can't do either one of those.
My goats are dry at the moment. So I took 1/3 of my milk kefir grains and froze them, 1/3 of them I dehydrated, and 1/3 I am trying to change over to reconstituted powdered milk. I don't think it is culturing the powdered milk just yet, it seems to still just set there until it naturally sours. But, it isn't dying!
Healthwise it is good. But tastewise, it just can't compare to good buttermilk, or yogurt cultures! It works great in smoothies or for baking though.