I recently put Ultimate HDLs on the tweeters and MK III on the woofers of my Audio Note kit 3 (E silver) speakers which are bi wired with Lexus and hooked up to Audio Note Soro SE amp.
The improvement is obvious and I agree with others. Layers of hash are removed throughout the audio spectrum, I am more able to hear more 'into' the music, deep into the smallest corners - information is more obvious, spatial cues are more apparent, bass is less tubby and everything is more defined.
I do sometimes wonder if the sound is less open than before but I suspect my ears are just missing all the extra grain in the high end. I have no desire to switch back just yet but will eventually and will report back if I find any fault with the HDLs. I do not expect to.
At this point they are among the most significant tweaks I have done. Almost to the point of not being a tweak but instead a component upgrade.
FWIW, if I could remove the HDLs and instead upgrade my AN-VX ICs to the superb AN-VZ ICs I do not think I would do so even though the AN-VZ is the best IC I have ever heard, the HDLs are a bigger step up allowing more information thru (come to think of it I would like to hear the AN-VZ WITH the HDLs hooked up!)
That is all. I am so happy with the HDLs I wanted to share with others. Several years ago I read a rave review of them in TAS and have wanted to try them ever since and am very glad I did and encourage others to do the same.