You have to install both.

For more detail, the M4 planet had way too much cut from it to really be able to "restore it" the same way everything else was done for TSLRCM. M4 had to be bult more or less from the ground up, with the barest of information on what was supposed to even happen there, as it was cut early enough that there wasn't a whole lot even completed to begin with, outside of some voice lines, and a general idea of what the planet was about.

TSLRCM did a lot of restoring and fixing with what was already there on the disk. M4 had to be done effectively from scratch.

And the difference is major enough that it justified making it a seperate project. Especially because, while I think it's well done considering what it is, your milage may vary with it.