I can't find the option to select it in my main menu, it looks just like the default. I checked to make sure it was installed in the right folder.
If it is in your <WFaS installation folder>\Modules\PreBattle O&D\ there shouldn't be a reason that it doesn't show up in the launcher (your install folder would default at C:\Program Files (x86)\Mount&Blade With Fire and Sword\ or C:\Program Files (x86)\Steam\steamapps\common\mount&blade with fire and sword\ if you have Steam and the installer should find either). Depending on your OS, perhaps you need to remove the ampersand '&' ...but until dHErblay, I've not had anyone mention that before and the mod's been released and installing to the same folder for almost a year and a half.
The main menu in game will look the same when you select "PreBattle OD" instead of "Native" in the launcher (the pic on the launcher will change though). Once in game, your character needs either 1 point of tactics to see any new pre-battle options and 2 points to see them all. There will be a new "mod options" choice in your camp menu right away, however.