Our software supports Duet Display on iPad Pro and runs smoothly in 60 fps. A little latency can be expected due to duet connection, but not should normally not be an issue.
Best result can be expected connecting the iPad Pro using a USB C cable to the Mac.
If the iPad is connected through to your computer using WiFi display lag may be encountered, depending on your WiFi generation and the actual network bandwidth.
The non "Pro" iPads are officially not supported, not tested, and we can't guarantee that it works.