Single driver speakers. Are they worth considering ?

I have an 8 watt 300B system (Wavelength Duetto), and single driver Stein Music SP 1.1 speakers.  I have very much enjoyed the Steins for going on five years (a record for me).  I cycled through many traditional speakers prior to them, and even during this period have scratched the itch to buy and try Devore 3XL, 0/93, Daedalus, and Audio Note AN/J. 

I do of course notice less bass response as well as a loss of some treble.  That is why I thought I might be able to improve upon them.  And for a week or so every one of those trials convinced me that I made a good choice.  Then, I put the Steins back into the system and very quickly decided that the Stein's presentation is more organic, realistic etc.  The immediacy of single driver speakers is very addicting.  For me they give me a "band is in the room" vibe better than the other designs I've tried.  Holger Stein is known for effective, natural and physics-based tweaks and his SP 1.1 design considerably tames any downsides to the design. Your mileage and ears may vary.

I just recently found a set of Musical Affairs speakers with natural wood cabinets and PHY Sag drivers, and am looking forward to my 2nd pair of single drivers!

I have a friend here in Vegas with the AER BD5. It is an insanely expensive driver ($45K/pr) but the sound is incredible. I need to add that is is augmented in the bass as it is on a 200hz LeCleach horn but absolutely stunning regardless. I have never heard a single FR driver sound that good. Everything else has some issue somewhere. If you do not have the budget or equipment then you have to accept some compromise somewhere.

I once owned a pair of Rethm speakers with Lowther drivers. The problem was a thin sound with no bass. Adding a Rel subwoofer didn't help much. There was always a dip between where the driver left off and where the subwoofer picked up. 
Check out Bache Audio. I have the Tribeca speakers.  These are based on a modified wide band driver that covers the range from 700-10K, augmented by a super tweeter and 2 woofers. The wide band driver is directly connected to the amp (no crossover). It's like a single driver but with better top and bottom end.

The best single driver speakers I’ve heard are the Rethm. 

The Rethm speakers I’m referring to are the current version that does not use the Lowther drivers as mentioned in the post above. I do not know the brand of driver that is being used, but there were none of the issues that jdal mentioned in his post. But the model speakers I’ve heard were the Saadhanaa’s.  Very clean, strong and full bass.