Zone Focus

Many articles discussed sharpness. Yes it's important and many may will disagree with me. 

But do you need to track the eye and spend money to purchase new cameras, "gun site" accessories? IMHO No.

Consider zone focus. 

For me with moving subjects I use Photopills DoF pill to decide will the subject be in focus.

When I'm using my 75-300mm glass wide open at f/6.7 and estimated distance of 100ft my DoF is over than 6 feet. That's enough for me to capture many subjects with acceptable sharpness. At f/8.0 DoF is 8 ft. That works for me. YMMV.

For those not M43 shooters need to consider the sensor size. Using a full frame at 600mm it would cut the DoF about half.

 DoF Simulator

PhotoPills DoF Pill

Choose your aperture

My DoF Rant