Braking Factor

It helps to stop fast quad rotation. Also in many cases allows to have lower D (good for motors)... Quite nice thing. Since it depends on your setup, you need to try it yourself and pick a number between 0% (old kiss) and 100% full ultra.

Acceleration Factor

The new feature allows your quad react faster on the fast stick movements. The allowed values are between 0% and 100%.

If you set 0% - nothing changes, and quad will fly like any previous firmware (default).

If you add some value, you will feel increase of the quad "snappiness". Start slow, and set to whatever fits your flight style and rates.

For normal casual pilots values 25-50 is a good range. For extreme freestyle 80-100. Find your value :)

You can also change it from OSD (FC Setup, Page 4) or from crossfire lua.