Single driver speakers. Are they worth considering ?

single driver speakers have very poor higher frequency sound and cant do bass. That is the price you pay for a bit less comb filtering in the mids.

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. 

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.  

The Comb filtering is what causes dips off axis.  Hence poor dispersion.