Did not like the SEMA-1 external mic
I tried the external mic. When mounted on the hot shoe, it was worse than the internal mic because it magnified the sound of focussing, even with manual focus of kit lens. When taken off the camera, it was ok but not great and not worth the hassle or the cost, or having to give up the viewfinder. I'll be sending it back and looking into an external recorder and learning how to sync when it's really important.
On the positive side, this makes the choice between the mic and the viewfinder a lot easier!