DMZ is a misnomer in most (if not all) consumer routers. There is no “zone”, after all. The correct term is “Exposed Host”. This clarifies things a little.
The Exposed Host is not separated from the rest of the network. It still resides on the same broadcast domain. If it were to be compromised, the attacker would have unfettered access to the local network. (Unless it is otherwise separated.)
Also, if any “internal” services are running on your Exposed Host, they would suddenly be Internet-accessible.
A better way would be to set up a VPN service (like OpenVPN, requires only a single TCP or UDP port) and forward ports for this service only.