Just a quick update - I tried using the MT300A with firmware as a OpenVPN client device. I was connecting to my home OpenVPN server. The MT300A was connected via an Ethernet cable to a router in a hotel.
The MT300A with firmware 2.27 was unstable and had difficulty connecting and holding an OpenVPN connection. I re-flashed back to the “old” stable 2.264 firmware and everything was then OK.
The 2.27 firmware appears to have introduced problems with the OpenVPN client functionality.
I am really grateful that you support your devices so please take this as constructive feedback !