G'day Flaming Pig (nice nick!)
My experience with Bw (X/O) DBEs is quite positive. I've used them in small numbers in a Nikephorian Byzantine army, and they usually did the job for me that I needed.
For me, the big strength of the Bw (X/O) DBEs is that they only count as 1 ME per DBE while still being quite formidable fighters. Yes, that means you're paying 10 AP per base, and it means your commands will be smaller in ME than they would be if they were Pk (O). However, this means that losing the DBEs has less effect on your army's morale than losing an equivalent AP of Pk would.
What this means is that a good command structure involves leading the attack with the Experimental Phalanx, and using, say, Kn (F), Ele and baggage as support to bulk up the command's ME. If you design the command the right way, it's possible for the command to still be alive, even if the Experimental Phalanx elements in the command have been wiped out. In my books that makes them quite powerful.
I've used a similar powerful-but-expendable system with my Sub-Roman British - lead with the 0.5 ME Irr Sp (I) and rely on weight of numbers to overwhelm the enemy, even if the army contains troops which normally Quick-Kill the Sp, while the elite 1 ME Irr Cv (O) skulk behind the line.
Good luck.