well all speakers are omnidirectional below about 200 hz
and all are laser beams above 10 khz or so
it’s really how you get from that 200 hz to 10 khz that separates them
with better designed speakers it’s smooth sailing
with poor ones it’s a bumpy ride
the horn i linked would probably not be that great because as i said i think they made a trade off in favor of efficiency, low end boost and compact size over sound quality. which makes sense because for PA / Prosound use output to size and weight ratio trumps most other considerations.
go to 5:15 in the following video from JBL Museum:
that’s sort of the dimensions a midrange waveguide needs for no compromise performance. that waveguide is 30" wide. if you’re not willing to go that big maybe ( in fact likely ! ) indeed some other approach is better in your case.
AudioScienceReview ( in the actual speaker reviews, not forums ) has some decent discussions on directivity issues …
also Spinorama:
has a lot of directivity data on different speaker types that should help you determine whether you indeed prefer wide directivity or simply smooth off-axis and power response.
it is quite possible that you indeed prefer wide directivity speakers at least in the room you are listening in.
on one hand more directional sound should mean greater ratio of direct to reflected sound and thus better imaging … on the other hand some people might have a preference for “live” sound, that envelops the room in an “ambience” rather than is localized between the speakers.
you should certainly build for your own subjective preference otherwise there is not much point in DIY …
final point is you can always add surround channels if you feel like you could have benefitted from more reflections in the room … on other hand you can also add sound treatment to have less reflections …
adding surround channels would probably be cheaper than proper room treatment …
though proper room treatment would go further towards the goal of ultimate sound quality …
so yeah it’s all a system as i said before, including the room.
you will probably make mistakes ( everybody does ) - just try and leave yourself a path towards upgrading later. basically make sure the system can be torn down and rebuilt in many other configurations if possible so you have a foundation from which to tweak your way to your preference.
i know that didn’t help at all but i had to say it anyway.