Interesting, Mose - this is the second time I've heard this in less than a month - even the same potency. I see that you are from Germany, and I heard this from someone in Switzerland, so perhaps the information is just now getting to the USA.
I sure like the idea of using Ledum since it should also offer some protection from infection if you are bitten!
Reduction in ticks is good, but all it takes is one that is infected.....
From everything I've read, it sounds like the trick is to make yourself or your pet smell like a plant or a flower - scents like Eucalytus, Rose Geranium, Lilly-of-the-Valley, and some Cedars can be very effective. But caution is always in order when using plant 'oils' on cats as they can be toxic.
Hard to believe such small bugs can cause us so much misery.
Tracy