Are Horn Speakers good or bad or simply a complete joke?

Horns are great esp. if you like the punch / slam / dynamics of live music. Setup is critical, but the rewards are very worthwhile. A forum archive search brings up 54 references to horns in the speaker catagory alone - I suggest you pursue that lead. Below I have pasted in the search link for you (first entry below links to the above-referenced 54 finds). Below that are 10 direct links to individual posts from the aforementioned 54. There is a lot of good info here:
http://audiogo5.iserver.net/cgi-bin/fr_srch.pl?0&1&procsrch&3&4&

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&989249073&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&988933562&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&986076653&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&981725620&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&980394513&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&979415558&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&973282698&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&969595915&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&936412039&read&keyw&zzhorns

http://audiogo5.iserver.net/cgi-bin/fr.pl?cspkr&922525017&read&keyw&zzhorns

Sean wants to snag my WHAT? Wow I'd better be more careful; I was just thinking about stopping by the radio shop & showing them off just to watch you drool! Maybe I'll only bring in one of them; that won't get you too far - hee hee.

I heard the Avant's in '99: no "cupped-hand" midrange horn resonance coloration was noticed although it was only a very brief audition. They're made out of some kind of a composite material.

As I said previously, setup is critical with horns. I'm also doing a similar mod-project (presently all on paper) of my Belle Klipsch's & still collecting the parts for this job. However as I've fine-tuned & upgraded my rig to a higher level of finesse, that cupped-horn coloration has significantly diminished to the point that it's no longer very much of an issue, even pre-modded. When talking "setup" I mean system-synergy: using the right matchup of equipment, cables, tweaks etc. It's a long-ish pathway to nirvana but I'm really very pleased, even prior to total optimization.

Todd, horns are certainly unforgiving as you say. If a rig has any upline problems, then you'll certainly be more aware of that when playing through horns. If everything is setup properly then the articulation & control, definition & detail are amazing indeed.
I haven't heard the RF line, but now I'm really interested in checking them out - thanks.

yeah she probably has multiples to choose from too :)

horns are ceratinly an "in-your-face" presentation: transient immediacy, detailed & very revealing are their hallmarks & some don't like that, although myself I'm hooked on their speed. They are in fact SO revealing that they will unmercifully show you any upline equipment flaws, so a clean setup is absolutely critical, which can of course be quite difficult & expensive to achieve. This characteristic may be considered desirable, or not, depending upon one's goals & perspective.