I enjoy listening to good omni's and the Duevel's are lots of fun. They aren't the most neutral or accurate speaker and they are little round in the bass with somewhat limited extension, but they do omni 3-D thing nicely.
MBL's like the 101E's do it much better but at a much higher cost, not even including the enormous cost of the right electronics to drive them properly.
If I had lots of money to burn I'd have two systems, one with Vandersteen 5A's and the other with MBL's.
I don't believe the Duevel's are quite at the level to be a good replacement for 5A's. They'd be more of a fun thing to visit for awhile. To me it would take MBL's to compete with 5A's and even then, it's a totally different sound that will tend to favor some music more than other
BTW, I am a Vandersteen dealer an a big fan of the 5A, but I've enjoyed listening to the Duevel's and MBL's on numerous occasions.