I have an FP24 which I sent to Sound Devices for checkout and repair this May. They replaced the return-level pots and the limiter threshold pots, "confirmed unit is at production spec, passed all factory bench tests" and the total was $76.76 plus shipping. Turnaround time was about two weeks.
I also have an MP-2 which evidently needed more attention: $128.65 + shipping.
Both units were sold to me in supposedly "like new condition" and I really don't think that any conscious deception was involved. In my experience this is a typical, normal outcome of buying used recording equipment.
--In general there's no technical advantage to be gained by using a balanced output to drive an unbalanced input, unless you balance that input (and then there's a huge advantage to driving it from a balanced source rather than an unbalanced one).
In any case you do NOT want to use the XLR outputs of an SD preamp to feed an M10 or any other device with consumer-type aux inputs, because the gain of the FP24 is too high for that. Even with professional recording equipment, when I use the FP24 or MP-2 I generally have to set the recording equipment to its least sensitive setting and run the SD preamps distinctly below the halfway mark within their gain range. And there are plenty of people who record louder music than I do, as well as some microphones that put out hotter signals than mine put out.
--best regards