The Device Setup app is designed to allow you to scan multiple devices in the most efficient way possible. With that said, we recommend batching your scans in sets of 25 or fewer devices.
While the app can handle scanning more than 25 headsets at a time, if any of the provisioning fails, you'll need to match the serial number to find the correct headset. The process of locating the failed headset will be easier with a smaller group.