With zero handoff (correct name), the controller decides when a client switches to which AP. However, this requires that each AP uses the same channel, which leads to interference, so this technique is not recommended if many clients use the network. The "normal" fast roaming is recommended. The client decides when to switch to which AP. With the Min RSSI feature, you can also let the AP control the whole thing a little.

Zero Handover and Fast Roaming are two ways of trying to solve the same problem. Zero Handover works (well) at low WLAN intensity. Fast roaming should work better than zero handover at higher WLAN intensity.

Zero Handoff can be turned on in the software, but should not provide any advantage over Fast Roaming.