Yes, I think it does help. I don't buy it all the time - usually when it's on offer - but I bought a couple of weeks supply recently after having a dodgy gut and things did settle down. My mum uses it to help with her IBS. I usually buy the 500 ml size and have that over 3 consecutive days. I don't have a particular time to have it but usually after food, as my body is hyper-sensitive to sugars, even the small amounts in the kefir.
You may find you are a bit more windy when you first start having it - hopefully nothing more than that but probably best to be close to home when you first try it - just in case!
As for brands, I would check the ingredients and sugar content. Unless you are having the plain stuff, some have a lot more sugar than others and stuff that really doesn't need to be in there, like maize starch. It will give you some protein - per 100 ml my one gives 3g, which is not much really and around 12% of the recommended daily calcium intake.