I guess you mean software feature difference. Could you share with us what you have seen or your exact concerns?
The two USB sticks have two different USB PIDs, Occasionally, you may encounter a piece of application that only accepts one stick, but not the other.
ANTUSB2 is the older version of the two with less memory. ANTUSB-m has the newer firmware to address some advanced networking requirements. But for consumer use cases, we don't expect any observable differences.
- Thomas