I am no expert, but I will assume that if you mention a tombstone we are talking about a horizontal or a vertical with a 4th. As I see it in that configuration, 0 to 90 to 180 to 270 (angle vise) is the same as 30 to 120 to 210 to 300 (flat parts) in the sense that each index is 90 degrees. You might lose a tiny bit of time going to 30 and coming back from 300 but if you’re clever you can minimize that time. On the other hand, not buying 8 angle vises per pallet could be significant and avoiding the vise form factor generally allows more parts per face of the tombstone. All of this is predicated on the scant information you have provided so YMMV.