What is your opinion of single driver speakers

I run Konus audio, Essence speaker's.

They use the Jordan JX92 driver's, I absolutely love them. Fast, detailed, superb imagery, and good to look at, (which means the wife likes them.

They are compact for a floor standing design, quite wide but the cabinet is just 4" deep, so very room friendly. 

Bass from the 4" driver with its folded labyrinth is plenty for my needs, but my listening room is only small. 11' x 11', so may be an issue in larger rooms

In some respects, co-axial driver speakers, like Tannoys, have similar sound as systems employing full/wide range drivers—a vivid, lively sound.  But, most full/wide range speakers have higher efficiency, making them better suited for use with low-powered tube amps (the best sounding amps), and tend to be better at low volume.  Still, a Fyne F 1 coaxial is a speaker worthy of serious consideration.

I have Concentric drivers in my Tannoys and they are remarkable. The sound is from a single point source which producing amazing soundstage.

I bought a pair of Charney Companions with Voxativ drivers last February and I like them better than anything I heard at the Capital Audio Fest last month. They have a liveliness and presence that is better than any other speaker I have heard.

I have a pair of Charney Maestros with Voxativ drivers which I picked because I needed something relatively compact intended for corner placement (i.e., not Klipschorns). Great bass for the listening I do/my preferences, and I can only notice the very lowest of the lows missing on a couple of reference tracks. And they go way louder than I could ever want or need on 8 watts of 300b SET power.

I don't have experience with other single driver speakers.