Single driver vs traditional 3 way loudspeakers

Not any tweeter ,  we are using top of the line supertweeter  Fostex EX line . . we try to use DavidLois, vox, clone.order one pair ebay and Compare to 2145 TB,  decide to stay TB, and DL sold.  for my expirence measuring and listening , whizzer cone little differences, diff resonance depending of size and configuration , but using same idea, on resonance fr, got peak and go down rapidly to 10hz, definitely much more worse than tweeter, but some folks like it and enjoining ,   

Well as a  speaker lab, I know costs come in as a  factor
$250 vs $550.
Sound is very close, so good move.
But in my case, I prefer the DL over the TB. 
+ as i mentioned, perahps , can't completely recall, but i do remember the Tang Band's phase plug did exhibit a  little beaming.
Which is why the W3/W4 have this spiked PP.
The DL does not have as much beaming so the sweet spot if not a issue as with the TB2145.
IMHO the whizzer is not the issues in past Foxtex/Lowther models. 
Its the material used to make the cones and also the inner construction/magnet type that made the early WBers (pre 2010) have some coloration.
The Whizzer performs excellent as it gives mids/highs a  bit  more openess , dispersion and sound stage. 
I must have a  whizzer in  a  W6/W8
In a  W3/W4 whizzer not  needed. 
My DL W4 has a  whizzer , but its really tiny and  voices accurate.  
The DLVX8 whizzer is a work of art and technical  achievement. 
Some chinese tech geek really cloned the AER/Vox with great success. And am I glad he did. 
Saved me alotttt of cash. 

Will be a interesting shootout the TBW3/1878  VS the DLW4
Both will remain, regardless how the shootout goes. 

Ok , we have different point of view on whizzer ,  for me whizzer cone is parasitic element came to stereo hi end from cinema-pro era, where was used huge cone driver with whizzer cone loaded Tube, The freg 8-10KHz
good enough fo quality sound in cinema. There is only one benefit for Whizzer ( mechanical tweeter)  no crossover , no capacitor , no any phase distortion,  Many audiophile like it ( inc you liked it) , so good for you,   

But when you consider AER/Vox/Festrex all 3 big WBer labs employ whizzers.
They must have tested with and w/o whizzers.
To me its not important whizzer or no whizzer, only the acutal sound matters to me. 
Still waiting for your imput as to the TB 2145's beaming effect.
I could swear I heard soemthing of that affect in my 2 day  testing. .
So if the 2145 does present some beaming,, well then yeah no whizzer  *IS* a  problem.
Which is why I think they designed the spiked PP in the W3/W4's. 
I mean to me beaming not a big issue as i am sitting in one spot,, HOWEVER if I can find a  speaker that has much less beaming,  and sounds on same hifi level (as does the DLVX8) well then I'd rather have the less beam speaker.
I know you want to defend the 2145 at all costs, as it is your main speaker in   the design.
Had I made more extensive testing of the 2, I might be able to find reasons to place the DLVX8 above the TB2145.
My review states *nearly identical** I am retracting now, the DLVX8 **I prefer over * the TB2145. Close call, 
But if only 1 gets the cigar,
 well then
DLVX8 gets the  Cuban. 

Mark Audio no whizzers
Fostex's top of line, whizzer.
https://www.madisoundspeakerstore.com/approx-8-fullrange/fostex-fe208ns-8-full-range/

No
This is Fostex's top line 8 Sigma
NO whizzer.
https://www.madisoundspeakerstore.com/approx-8-fullrange/fostex-fe208ez-8-full-range-sigma-series/