Using them to program your robot plant-watering robot is fine but using it for any kind of internet connected device more complicated than that is probably a bad idea.
I'm having trouble finding/defining iptables rules that can forward IPSec traffic from a dd-wrt to a server acting as a VPN endpoint.
dd-wrt does not support IPSec (not without recompiling and having to fiddle with a bunch of stuff) so that's why I was thinking about terminating in a server acting as VPN endpoint.
PS. PPTP is not a consideration due to its security flaws.
I did this with an old Mac Mini that was acting mostly as a media server. My router wasn't compatible with TomatoUSB, so I went with what I had. The toolchain was a bit different since OSX uses the BSD networking toolchain rather than the Linux iptables & such.
Edit: s/GNU/Linux
I do this with an old Acer Aspire One.
I wish the author explained some parts a little, like dev tun vs tun0.