If you use a VPN to counter a man-in-the-middle attack through a public Wifi hotspot, you would effectively be trading one evil for another. Most VPN's are exploited and used as

honey traps already, so it would be stupid to do either. Use Bitcoin on a private network and use Tor to access these services. No method is 100% bulletproof, but you stand a

better chance, if you use Tor. Linux is also less susceptible to attacks on the OS side.