What is the difference between cross band transmit&receive and repeater?

We know Ailunce HD1 has the cross band transmit and receive function, and Retevis RT23 has the cross-band repeater function. we know they all can set TX and RX frequencies of different bands in one channel, but do you know what is the difference between cross band transmit&receive and repeater? 

1. Different work mode

when we want to set the cross band transmit and receive channel on Ailunce HD1, the work mode is the simplex mode, but Retevis RT23 is working in the repeater mode.

2. Different QSO range

Ailunce HD1 is still working in simplex mode, so its QSO range is determined by the Ailunce HD1 itself and the QSO distance isn't very long. but if Retevis RT23 is working in the repeater mode, its QSO distance may be very larger. because the repeater always has the higher power to communicate hams from the further afield.

3. Different QSO purpose

Ailunce HD1 is the dual standby radio, but why do we need it to support cross-band transmitting and receiving? It's because when we want to do cross-band transmitting and receiving, we always have to change channels all the time. it's so troublesome. the cross-band transmitting and receiving of Ailunce HD1 can solve the problem perfectly. 

For cross-band repeater of Retevis RT23, it's used to expand the QSO distance.