Single driver speakers. Are they worth considering ?

Cal,
Agree .
The PHY-HP is a legendary paper cone driver created by the late Frenchman Bernard Salabert. The 12" version in particular is held in high esteem for superb sound8 quality. The Cube Audio Nenuphar is a very different design and approach which by all accounts extends deeper and goes higher than the classic PHY.
Charles

I can't remember the name of speaker brand that uses 10" PHY driver and optional super tweeter. Or maybe there are a few brands.

Hi. I have done some short term  listening to the Cube Audio Bliss, Magus and Nenuphar at a local retailer in my area. I have never been attracted to single driver technologies as my past experience with a few designs indicated a very thin, one dimensional sound that I simply was not interested in. Unfortunately, I only had approx. 30 minutes of time to spend, but I will say this, I will come back for another  audition when time permits. There was something very different about this brands general sonic delivery. 

@inna,
Ocellia and Tonian Labs are two brands that have used various size  PHY drivers. There were probably a few more. 
Charles 

@vinylbrother, 
If the occasion arises for further listening to the Cube Audio speakers (Especially the 10" Nenuphars) please share your impressions if you do not mind. 
Charles