I'm using Valvoline DOT-3/DOT-4 Synthetic. No issues. Whats nice is synthetic doesn't absorb water like regular DOT-3 Fluid. It pools it at the top of the fluid reservoir.
(And Yes, Valvoline DOT-3/DOT-4 Synthetic can be mixed with conventional DOT-3 and DOT-4 Fluid Without any ill effects. Just it wont have the full synthetic effect of not absorbing water.)