No, those caps are not better for treble bleed per se. I guess you are still not getting the entire picture clearly.
Treble bleed mod has been discussed plenty of times already. It basically allows you to retain the treble when you back off the volume knob. I'm sure you've noticed how when your treble bleeds away when you roll off the volume from the volume knob.
And about the vibration dampener, yes, it works for me. I can hear the difference, so I can say it works for me.
Mike recommended it to me, and after trying it out extensively at home, I'm surprised at how this little thing can make such a difference.
Basically, it dampens the stray vibrations from your tuning post to your nut. The crucial vibrations emanate from nut down.
You clip the gadget on right above the nut. And obviously, if you use a FR equipped guitar, there's no point in using this.
I don't know the exact physics behind this, all I know is that it sounds better and the clarity of chords is improved.
Having heard our opinions and recommendations, I'd say that the best thing for you to do is to try the things out yourself. If you can hear an improvement, then get it. If not, then don't buy it, regardless of how good the product's review might be.