For $1600, you can get a brand new Novi 1000. The SN-93 is the old style Paxton and I don't really have much experience with it. If it were me, I'd pay the extra hundred or so and get a new Novi or A-trim.
BTW, the Novi 1000 flows better than the A-trim incase you didn't know.

Good Luck with whatever you decide.