I have a confession to make. I have never tried the C-AF function on my EM5 Mk1 cameras. I assumed it was crap. pretty much un workable and pointless.
Continuous AF on most early mirrorless cameras relied on re acquiring the focus continuously, without the benefit of phase detection, predictive AF. This means in practical terms, that the camera is always hunting "from scratch" for each frame and unless the focus and shutter fire are nearly instant and in tandem, the focus has shifted. Nikon's V cameras were the best early, partly because their sensor was smaller giving more DOF at the same magnification as other cameras.
Olympus, Fuji and panasonic lagged, Sony showed some signs of getting it right.
On a shoot last year, I needed to follow a slowish moving subject, coming towards me. Not even setting CAF, but relying on the native speed of the first capture, I mated the OMD EM5 mk1 and 40-150 f2.8 (brand spanking new) and got poor results. It turns out that there are focus accuracy issues with non firmware updated EM5's and the 40-150 lens also, but the miss to hit ratio was very poor. My critical thinking at the time was poor as I only left hospital a short while earlier, was weak and unpracticed.
The lessons relearned were; know your cameras capabilities better, don't use new gear untried and don't forget old skills (MF etc.).
Last week I had a chance to try CAF out. Surprisingly it was not rubbish (I am often surprised by the EM5, even now). I think the only real difference s the continuous re focussing rather than the limitations of one shot focus, then re focussing. Why have I not used it before? No need for most of my work and my early experiences in a camera shop where I worked often ended up being in direct comparison to super fast tracking cameras like 5D mk3's.
It tracked a fast moving 3 year old at reasonably close distances and a series of speed boats at about 100 meters, all moving quite fast. There were misses, but there were plenty of hits also. Would I advertise to shoot sport full time? No. I will however trust the camera's (especially the newer Pen) to be faster than me in tracking situations and chase sport when a newer PDAF camera comes along.