Yes you understand me correctly.

For every models, you need to install gl-tor manually. But I may be wrong. If there is Tor already you do not need to installed.

For 16MB models, Tor is not pre-installed and Tor cannot be installed directly because no space. So there is a Tor firmware built for 16MB models which removed openvpn etc.

Some users used exroot and installed software on USB storage and they have unlimited space to install packages.

I hope it is clear.