They are all digestive aids IMO and not weight loss solutions! Good for your gut. I'm not a nutritionist though- just read alot. You'd need to clearly check the packaging in terms of carbs/sugars etc. Kombucha can taste fairly sweet, but apparently is low sugar.
I've tried multiple kefirs. I often buy the Biotiful, plain flavoured one. There are fruity flavours, but they are much higher in sugar. I've tried a few which tasted like fizzy, off milk- so not pleasant at all. Trial and error I'm afraid.
Kimchi- again, I've tried a few. Some are rather spicy, which I don't mind, but I sometimes struggle to know what to eat it with. Or do you just eat it from the jar?
I've never just drunk cider vinegar, but use it in dressings, marinades etc
If its good gut bacteria, there is also sauerkraut, which is also easy to make yourself.