Tuning Collars on speaker cables - concept and any good?

Hello all,
I was wondering if someone can tell me what the effect is in the "real world" of having tuning collar on speaker cables. Are such tuning collars any good (for example Stealth Audio offers them)? Is there any downside by having them?

It would be great to hear from other fellow goners who have first hand experience with them, if possible with Stealth Audio cables.
Cheers and thank you for sharing your information
Mike