New Olympus Promotions Free & Discounts
The lens is worth having if you shoot telephoto; it's a good quality fast-to-focus lens. Note that, unlike the 12-50, it is not weatherproof.
The MMF adapter lets you use 4/3 (as opposed to Micro4/3 or M4/3) lenses. This is useful if you want to access the 4/3 DSLR lenses that Olympus (or Panasonic) make. Some folks use this to access the larger aperture zooms - e.g. the 14-54 f2.8-3.5 Mk2 zoom or the 50-200 f2.8-3.5 zoom. Neither of these will focus nearly as quickly as M4/3 lenses, but since there are no M4/3 equivalents yet, they can be useful.
The other adapter lets you use older manual focus Olympus OM mount lenses on the M4/3 system - no autofocus, manual setting of aperture only. There are $10 alternatives on eBay that work well if you want to experiment with this capability.
My 2 cents worth? I'd recommend the $150 extra for the 40-150 lens - it is incredibly lightweight for its range and greatly expands your capabilities - if you want to shoot telephoto. I'd consider the MMF-3 adapter only if you really want to use a specific 4/3 lens, otherwise, I'd get the flash unit as my free bonus.