There are two versions of One Man Band: Originals and Essentials.
Originals has been released the first time in 2002 and since then a lot of features have been added.
Essentials have been built more recently, mainly to provide a Macintosh version but is also available for Windows.
In short you might say that Originals is a typical Windows application (lots of options) while Essentials is typical Macintosh (easy and intuitive). Both concepts have their advantage.
Although a lot of the Originals features are omited in Essentials, it does have some major inprovements. Originals is not discontinued, both versions are supported in full. The choice is easy if you are a Macintosh user, only Essentials is available for OSX. For Windows users the choice is difficult, but when you buy one you will get an offer to buy the other one for only US$ 12.50. You can always switch or use both.
First a list of features in Originals that are omited in Essentials.
VSTi and DXi support. OMB Originals is not the best VST host available. Those who invested a lot in VST instruments mostly prefered there favourite host and connected to OMB with virtual MIDI cables like LoopBe. It is advised to do the same in Essentials or connect the softsynth as standalone synthesizer instead of VST pluging.
STPL. Although this is a much easier way to modify styles in batch than using a regular programming language, there will be a learning curve if you never used any programming language before.
Instrument definition files (Sonar .ins). Installing an Ins file with the desciptions of the instruments in your synthesizer makes it easier to read than the Patch/Ctrl0/Ctrl32. But then you will have to find an Ins file that matches your synthesizer.
Song window (use Sequencer window instead)
Arranger window (use Sequencer window instead)
MIDI keyboard window (use Live window instead)
PC keyboard1 window (use Live window instead)
Karaoke window (buy Serenade if you need this)
Importing and exporting style tracks and parts (copy and paste from the Sequencer window to the Style editor instead)
Convert MIDI files to styles. In Essentials you can copy and paste parts from MIDI files to styles. You will have to do some more editing in Essentals that was automatic (though not perfect) in Originals.
Synchronization with other sequencers thru MIDI clocks. (In stead create a MIDI arrangement in OMB and then continue to work on it in you favourite sequencer or DAW)
Things that are improved in Essentials.
Available for Macintosh.
The actions that can be assigned to computer keys while playing Live, are not restricted to certain panels or windows. You can create your own menus with any combination of one-keystroke actions. Menu levels are unlimited.
The character fonts in the Live window get larger when you maximize the window, making it readable from a larger distance. You don't need to have the monitor right in front of you while sitting at the MIDI keyboard controller.
Increasing and decreasing the loudness effects the volumes instead of the velocity.
In the presets you can specify wether properties should change to a specified value or remain unchanged.
A recorded sequence in the Live window can be pasted into the Sequencer window, including the Style/Variation/Chord/MultiVoice information. Then the sequence can be played with different styles and multivoices.
When a sequence is played with a different style then the length of intros and ending is adjusted to the style automatically.
A staff view in the sequencer and style editor.
Easier interface for the sequencer with tabpanels for the different views.
The arrangements are saved in standard MIDI files. You can load the MIDI file in another sequencer/DAW, do some processing, save it, load it back in OMB and still have the Style/Variation/Chord/Multivoice information available (they are contained in markers).