Spar urethane has all the good looks of polyurethane plus major durability. I'd never use polyurethane on a call that is intended to get wet and bumped around in the field when spar is available. Another good finish is WaterLox, which is polymerized tung oil.
As far as safety, you're getting more nasty stuff in your mouth from BLO than you will from spar, laquer, poly or most other finishes.