Even at 5-20% that's still not bad.
All that aside, I'm not sure I understand why you seem determined to keep someone from trying this, when other women have used them and been very happy with them. Just because it didn't work for you doesn't mean it's not going to be good for others.
Of course your opinion and experience are valid, and I'm sure the OP is glad that you shared them, but other people do have other experiences.
DH married for 12 years, parents to 7 small people
Five of these:
and two of these:
including our newest addition, born 26-08-13