No problems with my Texas kefir, still use some almost daily. No allergies, although some people have sinus problems with dairy. I also started taking "bitters" a German thing to help digestion that tastes of licorice? And also brush teeth with dental healing essential oils. Last dental visit the hygienist remarked "no stains, tarter or bleeding anymore. What happened?"

I think real homemade kefir crowds out the harmful bacteria usually found in the mouth that causes disease and bad breath, coated tongue etc. It's a natural antibiotic. People with Candida or SIBO might have issues with taking some kefir at 1st?

Also good to quench the 'burn' instead of cheese or milk if you get hold of a pepper you thought was not that HOT LOL

Kefir "grains" as an symbiotic colony can't be compromised normally, except maybe by molds if not stored correctly. Live grains can be stored in well water for over a month.
It's like the SF sourdough culture. I've kept a culture pure for years and only use it sometimes to make waffles. It always works the same.

Note: flavor and thickness of kefir can vary depending on the temperature of fermentation and the milk used like "Promised Land" Jersey Cows whole milk. This is explained in the FAQ