Yes, it is backwards compatible to MoCA 2.0 & 1.1.
The MoCA 2.5 device will only communicate with each MoCA device at the max speed of that MoCA device on the network. For example on a mixed MoCA network:
ECB6250(v2.5) > ECB/WCB6200(v2.0) = 1400 Mbps
ECB6250(v2.5) > ECB2500C(v1.1) = 270 Mbps
ECB6200(v2.0) > ECB2500C(v1.1) = 270 Mbps.
Note: This is the MoCA communications speed between MoCA adapters. This not the MoCA adapter connectivity speed to the computer or device connected via Ethernet or Wireless to each MoCA adapter.