MSM is a pure substance. It is just sulphur. There is nothing harmful in it. Many foods have sulphur in them. We just don't get enough unless our produce is fresher because the sulphur breaks down over time.
It is a powerful detoxifier and anti-inflammatory. It is used to heal scar tissue. It is extremely safe. I use lots of it all the time for pain.
I do see that there are a few websites spreading lies claiming that one brand is superior to others but these are all false claims. All MSM is the same.
Some people claim certain brands work better for them than others. But this is subjective.
It is all made from seaweed and is over 98% pure. The rest is moisture content.
I don't know where you heard these claims but they are all false.