[Edit: 4/14/2013. When I wrote this review, this item was well under 10 clams. Now it's double that. Which is WAY overpriced. You can get jars exactly like this and of almost the same quality at various dollar stores. It either seals tight or not, that's the only quality issue. This jar is simply not worth more than 10. Look around for the same type of jar, many folks make them, check that the lid and gasket are air tight, and save a ton of cash.]
Making kefir is so easy if you've got two of these. Put the kefir grain/culture in one, cover with milk, seal jar, let sit for a day on your counter, then simply scoop out the culture with a slotted plastic spoon. Seal jar and put in fridge, put culture in other jar, repeat!
There. That took less than a minute to read and do. Or, pay some online ripoff artist money to get pointless videos offering a more byzantine method that works not nearly as well.
Life is so easy when you take the time to experiment. I did and found this kefir method which I'll put next to anybody's. Cost: two of these (or similar) flip-top bottles and a slotted plastic spoon, which are a buck or less at any dollar store. Mason jars work too but are harder to clean and the mouth is not as wide. These are the best, believe it.
These containers are also perfect as cookie jars, storing grains (if in dark cupboard), etc. I love 'em; easy to clean, hard to break, last forever. I've had one for well over a decade and the grommet is still fresh, not hard. This brand is good but most are similarly fine. Just make sure to always wash the grommet inside and out.
Enjoy your kefir!