Jtwrace,
No,unfortunately never heard MBL, so I can't compare the sound.
I can compare the two designs however to some degree.
They are similar in that both are inherently omnidirectional using a single yet supplemented wide range driver.
The Ohms however are physically damped/attenuated in the wall facing directions by default to enable easier placement near walls, so their measured sound dispersion pattern is not purely omni-directional.
Also the Ohm Walsh wide range driver reside on top of the cabinet like larger MBL and German Physik for that matter and is supplemented on the high end by a directional super tweeter and ported to extend the low end, whereas I think the large MBL wide range driver is supplemented on the low end by a sub woofer.
Larger German Physiks, which use their own derivation of the Walsh design, are also supplemented like the MBLs on the low end by a sub woofer, I believe.
All these designs will claim a high degree of phase coherency from top to bottom.
Ohm claims that their near full range design produces most of the most important frequency range that most people over 40 can truly hear via the wide range Walsh driver used. The theory is that we lose our ability to hear the highest frequencies recorded in music as we age.
Ohm As and Fs utilized a single Walsh driver for all frequencies but rolled off at ~17Khz, according to the specs on the Ohm site.
Ohms and German Physiks use different derivations of Lincoln Walsh's original driver design (look up "Lincoln Walsh" on wikipedia for more info here). I am less familiar with MBLs omni design but from what I have read on their site it is a more radically different breed of omni design.
One a'goner here whose opinions I respect recently referred to the Ohms as "Blue Collar MBLs", which is probably a fair description in that Ohm Walsh speakers range in cost from $1000 to $6000 depending on target room size and finish, whereas big MBLs cost over $25000 as I recall, so some might consider the Ohms to be "giant killers" and all that goes with that designation.
Ohm is located in Brooklyn NY, USA. MBL and German Physiks are imported from Germany.