This type of material is scarcer than the value would indicate. They are becoming more popular and the value will increase. The duplex cancels are $10-$25. Yours has a clear strike of both the cancel and the censor stamp so it is probably valued about $20.
Here is an example with the APO number in the duplex killer (APO 709) with a value of about $20.
The machine cancels are much rarer especially with the APO in the flag. Here is an example (APO 701) value $75-$100.