Horn based loudspeakers why the controversy?

 You cannot get the same dynamic range with inefficient speakers. You can apply as much power as you want but you will not get as great a range between the quiet and the loud as you will with a more efficient speaker. 
That is why typically efficient speakers will sound more realistic at lower volumes.

I'm a fan of horns, though I currently don't run a pair.

I have some close friends who REALLY dislike horns, and instead of trying to convince or talk over them, I prefer to listen and understand their complaints.  Beyond the typical complaints about shout, some centers on the integration or lack thereof of such disparate drivers.  Even as a fan, I acknowledge and understand, though I've listened to more than a few "regular" designs that do as badly or worse.

One more thing...horns come in both front-loaded and back-loaded configurations.  Almost always in these discussions, we mean the former when we use the terms generically, but some excellent back-loaded horn products have come down the pike

 Everybody has horror stories about hearing horn's. I remember the first time I went to addition a pair of model nineteens. The owner had them hooked up to a solid-state Mac and proceeded to turn them up so they were playing at about 120 DB steady. He looked at me with a big smile  and said see how clear they are? He didn't even have them set up properly, had  them facing one another across the room. I couldn't get out of there fast enough. Thankfully down the line I had some reasonable experiences  and grew to appreciate horns greatly. 

 Regarding Altec A7's I had a pair for a while and after quite a few mods they can sound quite good.  

Well, being an owner of new Klipsch Forte III's, I thought I'd chime in. Had Magnepan .7's for awhile and really liked them. In my listening area I knew I was only getting about 75% of what they could deliver because of space considerations. Took the plunge on the Forte's (my 3rd pair of Klipsch over the years). I can say I am very pleased and frankly, pleasantly surprised. They are the most refined yet dynamic sounding Klipsch I have owned. They aren't for everyone but with my taste in music being primarily electric blues and classic rock (Yes spinning now) they fit the bill. One man's trash, another's treasure. Using a Rogue Sphinx with upgraded tubes with splendid results...

@analogluvr 
How exactly do you figure inefficient speakers can't be dynamic as all hell given robust power? That math doesn't work. Sure, many inefficient speakers are limp on account of torpid power, but there's nothing inherent preventing them from being dynamic. You accuse me of relaying outdated or inaccurate information, but what you're saying hasn't been true since the power wars of the 70's. 
No offense, but you and johnk seem to believe audio hit it's zenith in 1935 or there about and everything since has just been regression. No matter what anybody seeks, you two prescribe massive horn loaded solutions and low power tubes. Prescribe for me the fully horn loaded full range speaker that will fit within 2 or 3 square feet and is suitable for listening at 10 to 12 feet using modest solid state power that costs less that $5000. I think those are very common demands of a great many people here. You guys can't even bring yourselves to admit those speakers don't exist, much less appreciate that's not a practical solution for many. At least HR admitted the 936's came surprisingly close to the dynamics of the Uno Nano's so I know I'm not listening to a couple of compressed piles of junk. You and johnk and a few others talk like there's some vast chasm of difference and that no shortcoming of horns compares to the failings of dynamic drivers. It's frustrating to those who don't agree. And you guys just don't take no for an answer. 

The real irony to me is that the same people who vehemently argue for the dynamics of horns are the same who think vinyl is king. You don't get more dynamically compressed than vinyl. Why the big concern about your speakers dynamics when your source can't utilize the capability?