After quite a long time the Olympus PRO 40-150mm lens is back in Stock at Amazon US (Click here). And SLRgear (Click here) reviewed the Olympus MC-14 1.4X M.Zuiko Digital Teleconverter and writes:
It’s also extremely small, lightweight, fully weather-sealed and doesn’t negatively impact image quality or AF speed to a significant degree. If you own or are planning to own the Olympus 40-150mm ƒ/2.8 Zuiko Pro or 300mm ƒ/4 Zuiko Pro lens, the MC-14 teleconverter is a no-brainer accessory to have in your kit.