Can I use my account with several computers? Yes. If you configure your router in such a way that it establishes the VPN connection directly, then all computers attached to it are protected. This is possible e.g. with Fritzbox or DD-WRT.
That service says it supports PPTP, which is pretty common for VPN's, so if the new DGTeam firmware supports PPTP it should be pretty simple.Time to read the DGTeam release notes, or install it and investigate the options?