the downside to cargo flights is that they tend to be forgotten by ops control, and there seems to be very little concern for ontime performance, particularly when it comes to shorter turnaround cargo flts, meaning you can sit for hours waiting for loading to be completed.
Also the timing of them is generally back of the clock.
I agree its nice for a change, but only a few times a year. I recently did 4 cargo flights in less than a month, 3 of them on reserve.