The following is in the ArubaOS 8.5 Users Guide (and previous version Users Guides)
"Legacy 802.11a/b/g devices do not support ClientMatch. When you enable ClientMatch on 802.11n-capable devices,
ClientMatch overrides any settings configured for the legacy bandsteering or load balancing features. 802.11ac capable
devices do not support the legacy bandsteering, station hand off or load balancing settings, so these APs must be managed on using ClientMatch."
I hope this helps,