Single driver speakers. Are they worth considering ?

Evolution and progression does occur.  Someone's experience with a Lowther single driver speaker has little to do with hearing a Nenuphar or Charney. Faulty extrapolation. 
Charles 

I think you'd be better off with a Woofer-Assisted Wide Band (WAWB). 

It's like a full range, but with a woofer added.  One driver handles 300Hz to 20 kHz.  The big advantage is the crossover stays out of all the delicate areas, and from 300Hz upwards you have a point source.  Obviously plenty of cons to this as well.

I suggest if you want to try this out look into a Madisound kit.  They even h ave them for desktops.

Best,

Erik

I recall hearing a very well implemented single driver speaker based on an 8 " Fostex driver at RMAF a few years ago. I was really taken with the sound quality. One of the better rooms of the entire show.

There are some inevitable tradeoffs but this applies to "any" type of speaker. Multi driver/Multi crossover speakers have their own set of tradeoffs. It is always a choice of what compromises can you willingly tolerate long term and be happy.
Charles

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? 

Erik,

I've heard a lot of wide-band/full range drivers used very successfully in multiway systems.  Some were, as you discuss, assisted by a woofer, others were assisted by a tweeter (most commonly with large diameter full range drivers) and some with both a woofer and tweeter.  Most of these were custom-built systems.  An example of use of extended range drivers in multi-way systems includes the SoundKaos Model 42.  By using simple, first order crossovers and allowing the crossover points to be away from the critical midrange, fullrange drivers minimize the negative aspects of multi-way designs.