can someone confirm that both the AD9833 and AD9834 require reprogramming whenever they are turned off? which the recommendation to avoid this?
These devices does not include EEPROM or Flash, and the content of the registers will be lost if the supply is disconnected.
If you loose the power you have to re-program. To avoid this you must ensure that power is not interrupted after device is programmed. If you're looking for a device which you can program and it stays programmed (like some clock generators) you need to look elsewhere. For such application (and still using the AD9833/34) the best answer is to include a small microcontroller to perform the programming function every time power is applied.