Hello Greg,
Yesterday after spending a day I set up a VPN connection between my pfsense (2.3.5) and ar750s so I can help you with that. As you probably noticed when you import ovpn file the wizard adds incorrect options into the file - that is why you are getting the meaningless error "–secret vs " and manual file modification is required.
But honestly I don’t think it’s worth it especially if you are going to use it for work. The max speed over OpenVPN tunnel I have seen was about 12Mpbs up/down, the wifi 5GHz stuck at 54Mbps link speed, the latest firmware causes constant disconnects of wifi 5 Ghz clients (I saw another thread discussing this problem, so I had to switch back from 3.101 to 3.025), the SSH/FTP clients constantly disconnect and it creates real royal pain … In my case I redirect DNS requests to pfsense using “dhcp-option DNS” option, the VPN does not work after restart - i.e. the tunnel is set but DNS is not therefore there is no doman name resolution for VPN clients - to make it work one has to restart VPN tunnel manually after reboot. I wanted to install the latest stable release of OpenWrt (not 4MB version) - does not seem to be a simple process (the forum contains questions regarding this subject but not answers)
I periodically see in the log different error messages saying that openvpn daemon crashed - all this makes me think that I cannot rely on this small and cute device for anything serious. But I do like the fact that it has GPIO support and I can carry it in my pocket (I saw several reviews were people mentioned that as the primary advantage on this device - hello, guys this is a router and it should be reviewed as it) - may be I can use it to control my electronic cat feeder (at the moment it uses ATTINY85 + ESP8266), although it would be a very expensive alternative - I just bought it in Canada for 109$. Other than that this is a toy which can be easily outperformed by a much cheaper Raspberry Pi - just saying.
PS: the message was edited - spelling corrections.