I was flying the Curtiss Jenny yesterday; its instrumentation is bare-bones so there’s no turn/slip indicator, but I could definitely see by eye the effect of adverse yaw when using vs not using a little rudder.
During the roll, without rudder I see that the aircraft yaws a bit in the opposite direction of the roll, then afterwards starts turning as expected – while its heading remains more stable during the roll if I coordinate with the rudder.
Nicely done to the devs on that one. 
(Also, I highly recommend a head tracker like TrackIR for those open-cockpit biplanes!)