I'm not a fan of compatibilism mostly because their strategy seems to be to just redefine free will to be something very weak. Of course, most debates about free will are merely debates about what free will means.
If you start from that assumption, it seems like a foregone conclusion that free will doesn't exist.
As for the Miller-Rabin test, it's basically a case where you can get a correct answer with an arbitrarily low probability of error. So I guess the tie in is that just because our decisions are predictable (or at least mostly so), doesn't mean there isn't randomness involved.
I'm starting to suspect that I'm responding to an interpretation you didn't intend, though.