They are like any other piece of equipment in that they need to be used properly, with instructors who know what they are talking about guiding you on correct use. We use them in our Pilates class occasionally - the teacher guides us on how to use them, and they are beneficial. They offer enough resistance to be helpful but not too much to be damaging, if used correctly.
I’m so sorry, Luckygirl3 that your experience using one was so detrimental to your well being. It does sound as if your instructor was poor, and you suffered so much damage as a result.
They are very cheap to buy keepingquiet and are available in a variety of strengths - your healthy living instructor should advise you on which strength to use (and where to get it from), and this should be based on your level of fitness which I hope they have discussed with you.