Single driver speakers. Are they worth considering ?

KEF likes to do single driver point source speakers. It depends what you want. Single drivers have less highs but perfect dispersion. A 3way speaker has clearer sound but horrible dispersion. 

I'm not sure what Kef is a single driver but they do have the small coaxial or point source LS50 which is a 2 driver and nowhere near full range.

Not with a cone speaker, a coaxial is a great idea.. Some think it's the best..

A single coaxial driver, yes. Not my cup of tea.. I've heard some good ones though .. Tannoy Speakers..

Regards

You might be interested in the commentary happening over in this thread for the single driver cube audio speakers: https://forum.audiogon.com/discussions/cube-audio-nenuphar-single-driver-speaker-10-inch-tqwt-enclosure

Of all the true single-driver systems I've heard, the quarter wave back loaded horn systems of Voxativ and Charney are the only ones I really liked because they had reasonably extended frequency ranges and smooth response (not excessively peaky and rough sounding).  I am particularly fond of Charney speakers with the AER full-range drivers.  The Cube Nenuphar was okay too, but, its frequency response was not quite as smooth and natural as the other two and it lacked the upper bass weight needed for large-scale classical music. 

I don't consider coaxial drivers to be full-range drivers, they are two drivers built into the same frame and utilize a crossover like any other two way speakers.  But, they certainly can sound good.  The big Tannoy systems, like the Westminster, are very good sounding.  

I have heard a lot of fine sounding multi-way systems that utilize drivers intended for use in full-range systems as either a mid-range driver or the bass/midrange driver with a tweeter added on top.  I particularly like the Jensen M10 field-coil driver used as a bass/midrange driver with a tweeter crossed in at a very high frequency.

The comment above about full-range drivers having "perfect" dispersion makes no sense to me (I have no idea what perfect dispersion even means, never mind how any system can achieve it).  Given that most full-range drivers are relatively small in diameter for a woofer, they have WIDE dispersion at lower frequencies, but, given that they are large in size for a high frequency driver, they have a very narrow high frequency dispersion and need to utilize things such as a whizzer cone to attempt to spread highs adequately.  What they more or less avoid, as compared to multi-way systems, is comb-filter problems of two or more drivers interfering with each other.