Single driver speakers. Are they worth considering ?

Personally, I am not willing to compromise. Everything that has been mentioned in this thread that I have heard has been hopelessly colored.
Some people like the sound of these speakers. So I suppose what colored loudspeaker you like is a matter of taste. 
The only type of loudspeaker that can approach full range performance and avoid coloration is an ESL which the OP did not want to hear about.
Sorry. Just the way it is. Dynamic drivers are flawed in so many ways it is remarkable that some systems can sound as good as they do. Full Range? This is an illusion.  

One thing I forgot to mention. Specs for loudspeakers are extremely misleading. No 10 inch driver goes flat to 30 Hz in a normal room not even 10" subwoofer drivers. The measurement was taken very near field under anechoic conditions. None of these single driver systems produce any real output below 100 Hz and Ralph is quite correct. The driver flaps at 30 Hz just the same even though it can not project that frequency in a room. This doppler distorts all other frequencies. Roll off the bass at 100 Hz and the speakers will magically get cleaner. This is the same for large one way ESLs, removing the bass increases headroom and detail to unheard of levels. 
Many speakers make due with just mid bass. Our brains, tricky things that they are, extrapolate the fundamental. 40 Hz is more palpable than audible. Real bass you feel. If you do not feel anything there is no real bass. This is what makes live performances so incredible, the palpability of the music.
Big drivers beam treble which is fine as long as you sit square on with the driver at ear level. I have been living with beamy loudspeakers for decades. Ralph is right again. Whenever you see whizzer cones, run away! It does not matter how fancy the magnet looks. Whenever you see "fancy" in a driver, run away. Some of the fanciest looking drivers are the junk they sell for cars. If it looks good it must sound good? Right. 

Looks like fun to build but a lot of work for a single driver system. The bass is still going to doppler distort everything else the driver does. For such a large speaker why not do a two way transmission line speaker. There are excellent passive crossover designs out there or use a digital crossover.