Depends if your standby includes passenger flights. If it does, as PT Barnum put it - 'there's a sucker born every minute', as they can pump your flying hours up to max on the standby month plus pax you round the place and get 150hrs a month out of you easily. Plus you could enjoy constant disruption, less days off, less days at home. Could you imagine being the dogs body for the passenger fleet every month.
If the standby is for cargo only, and you will fly cargo only then maybe worth looking at.