As a someone who has space but not currently the budget for a large horn, I do agree that driver quality is important but only to a point. The 555 is a good example. You get all sorts of advice when you mention that you would like a speaker based around the 555. Many say only the original (with original diaphram) will do, others say GIP is better etc. As my budget may never stretch to the "originals" or even top quality repros, I have looked at modern copies like LM and a few other small shops. Reality hits when totalling the cost up and the driver seems to be the only real source of compromise when you can't DIY in a timeframe that makes sense.
It's a custom driver in a LeCleac'h horn. It's not very conventional as there are different design consideration vs a more typical horn but I can say it works extremely well, I'm very happy with the result and it does exactly what I intended. The speaker sounds like an excellent full-range driver with full frequency extension, the ability to play at much higher SPLs and a much better polar response.
I'm well aware of directivity matching but when your mid horn covers down to 400 Hz it doesn't matter anymore. Also, you'd need a big woofer for it's directivity to narrow by 400 Hz!
IMO the issue with these kind of speakers, either full-range driver or compression driver, is driver quality. Very few CDs or full range drivers sound good imo, but the ones that do beat out traditional cone 'n' domes for my tastes.