on mt300A running testing firmware (3.1000) the button (really it is a switch) does not toggle Tor on/off. Two reasons I know it is the switch:
Tor is working very good at 192.168.8.1:9050 when I use this as SOCKS
GL UI is available when switch is on either place.
It is not really a big problem because Tor is still working with SOCKS5 but maybe it is good to know. I did not test yet with OpenVPN, I really hope it is working to switch OpenVPN on and off.