I am going to Vietnam soon and make a decent amount of money betting on sports. Betfair Exchange isn’t legal in Vietnam, so I wondered if anyone in here has had luck with VPN’s in terms of betting from restricted countries? Thanks.
Personally, I wouldn’t mess around with foreign country laws unless you are absolutely sure you can.
You might get yourself in a similar situation as a recent WNBA player, only you aren’t famous and will be forgotten by the US (assuming you are from US).
A VPN should work fine so long as you always have it on and using your country’s servers.
If i were you, id leave a cheap pc on at home. Install parsec on it (software to remote desktop). Then from Vietnam, remote desktop to your own pc at home. Then do the betting on that machine.
You would want to prevent the machine from going to sleep or lock screen. You might want to setup an auto login plus a setting that automatically turns the machine on if it loses power and power is restored (wake on power, in bios setting), and if you really go the extra mile, connect the pc to a Philips smart plug or similar, that you can turn on and off remotely from your phone.
Yo hit me up with them winning numbers fam! 
Are you maintaining a US residence while you travel to Vietnam? Put a personal VPN server on your home network. For $100 +/- you can install a standalone Raspberry Pi running piVPN. See https://pivpn.io/ for more info.
Pretty sure Vietnam would be a lot more infamous if you get immediately thrown in jail for using a VPN.
Even China barely enforces their anti-VPN rules past trying their best to block them.
Fyi, we don’t throw people in jail for using VPN 
The risk isn’t getting in trouble for using a VPN, it’s getting in trouble for gambling online. That being said I don’t think there’s a huge risk of getting in much trouble for it in Vietnam, it seems like the most that would happen is a fine, but it’s always risky doing anything illegal in a foreign country.