Single driver speakers. Are they worth considering ?

Look at active  3 way with DSP controlled crossovers. 

They would happily measure them  if anyone wanted to send them or if the company did. They are interesting looking. 

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.

On single drivers the  frequency response tilts steeply upwards from bass to treble there's Beaming at high frequencies,  top end marred with ripples and IMD is a problem and they aren't full range. Other than that they should be fine. 

Build them with Hypex plate amps and use DSP crossovers you won't lose any magic just gain a better speaker.

I've never heard a full range single driver speaker, what's a good example of one for the OP to consider? It would need to produce listenable sound from 20hz to 20khz. Reasonable SPL and low distortion. 

There is also a YouTube guy, Erin's Audio Corner,  I bet he would like to put one on his new Klippel. 

https://www.erinsaudiocorner.com/

I see Charney claims 20hz-20khz with no roll off on the top of the line speaker. Some of the others in the 30's to 20khz . I see no measurements on their site to substantiate this. I don't suppose there are any third party measurements anywhere?