There was recently a thread on fredmiranda alternative forum on this very topic. Here:
Also given your link if you read the reviews you will see some comments on focus such as this one:
While I gave this lens a 4-star rating, this probably would not be everyone's rating because there are definitely two sides to this lens's personality on the OM-D on which I'm using it (with adapter). On the positive side, it's a really sharp lens right from f2 until diffraction starts being a problem. I've tried this lens with the Olympus 2X teleconverter, and even wide open I was surprised at how little the images was degraded; stopping down about a stop gets the image back to what I consider high quality. While the lens alone has what I consider a nice, smooth bokeh, adding the teleconverter does make the background "nervous". If rated on optical quality alone, I'd give this lens a 5-star rating.
Autofocus on an OM-D, however, probably deserves a 2-star rating at best. Focus is slow, and even once the camera thinks that the lens is in focus, maybe 90% of the time or more it's not...and sometimes not even close. There are times that the focus seems to be determined by distant features at the edge of the frame rather than the center where I am trying to focus. Mostly, the lens gets me near enough that it's simple to manually fine-tune focus, and the lens is sharp enough that I feel comfortable judging proper focus in the OM-D's viewfinder without a magnified view. Focus speed and (in)accuracy does not change with the 2X teleconverter. Basically, I'd consider this lens to be a manual focus lens with a near-focusing auto-assist on the OM-D.
In summary, because I don't mind fine-tuning focus and I like the quality of the images that have been getting I've rated the lens not quite perfect. However, on an OM-D, this is absolutely not a lens to be used for capturing action.