If it’s milk kefir, I’d say that there’s a wealth of research showing that dairy isn’t particularly beneficial to your health and my gut feeling is that you could replace milk kefir with other foods which are known to be health-promoting as well as flora-promoting and you’d be in a better place.
I’d also guess that sugar-free kefir would be ideal if you did decide to use it. Sugar seems like it quickly becomes harmful to gut flora and its diversity, so limiting it would be well aligned with the intent of building up better flora.
Overall it’s one of those things where you can ask: is it replacing something worse? i.e are you drinking kombucha which has very weak evidence of benefit, but some evidence of harm? Then it appears kefir is a good decision.
However, you can also ask if something better could take kefir’s place? This is a very individual thing. For some, they might be replacing Coca Cola with fruit juice, and if that’s the best they can manage than that’s fine - it’s still better.
If in your case it’s replacing milk with milk kefir, that’s also better. On the other hand, if you could replace milk with eating more greens for minerals, avocado for fat, and a blend of whole grains and legumes for protein, I suspect your baseline of health would increase and your gut flora would benefit more than from the kefir alone.
It’s all about “could I do something better?” because there are no silver bullets. Kefir, when added to a poor diet, will probably not provide a fraction of the benefit that simply improving the overall diet could.