The Kestral HR is more forgiving and works with anything, tubes or SS, high power or low power, HT or stereo only setups. It actually has better deep bass than the Shearwater HRs. The Kestrals are one of the best high value speakers I've ever come across.
The Shearwater HRs on the other hand are significantly better than the Kestrals in just about any audiophile metric you wish to choose. Much better transparency and imaging, highs are smoother yet more extended, very low coloration. Not surprising really since the Shearwater HRs use the same Scan Speak mid-woofer used in the Merlins, Wilsons, Vienna Acoustics, Pro Acs, and many others--all also more expensive speakers I would note. How does Pat do it? LOL
Having said that, the Shearwater HRs ARE more demanding of one's system, as a high performance speaker should be. I would not recommend them for HT use, as they are very neutral speakers in terms of balance--and with most HT source material, that comes across as "bright" when in fact it is souce related. Nonetheless, the right tool for the right job....The Kestrals more forgiving nature and warmer tonal balance would work better in this application. In addition, the Kestrals also throw a wider soundstage than the Shearwaters, which again would make them the better choice for HT. And they are easier to place in the room--just set the damn things down most anywhere and they sound great.
I also believe that to really hear the Shearwater HRs at their best, you need (quality) tube amplification, whereas the Kestral HRs sound just fine with nice modest priced solid state like Pass, Belles, McCormack etc...
What was the question again? LOL.....I have owned all of the floorstanding Meadowlark speakers except the top of the line Nightingales, I love Pat's speakers. As a final rough comparison, I would say the Heron-i's sound like "better" Kestral HRs, and the Blue Herons sound like "better" Shearwater HRs. But Kestral/Heron do not sound the same as Shearwater/Blue Heron, and I think that was Pat's intent. The Blue Heron uses the same Scan Speak mid-woofers as the Shearwater HRs by the way, but two of them, and an expensive gas piezo tweeter and Audax I think it is mid driver.
I would like to hear his little monitors at some point...