Re: How many device support MAC based access control?
Not sure what the question is. Can you rephrase? If the question is with regards to client support of the feature, the SSID appears as a fully open one. It doesn't require anything from the client, therefore all clients support this.
If you're question is "What is the max number of MAC-addresses I can specify", that depends on the RADIUS server so you'd have to check its documentation.