To take the talk back to the rhino
If the rhino dies, especially first turn or last turn the
ML ensures they have some say on the battlefield. Projects power would be a military euphemism.
Of cause in 2/3 of your games you can combat squad fairly successfully, unless you need the full squad for the task you want from them.
More importantly you are replacing the bolter. In the rhino you miss no firepower, if you stand still to shoot bolters 24'' you gain power, if you assault you still have pistols, it is only the times you move and shoot that you miss having 2 whole bolter shots.
You can try lascannon, which is cheap unless you do not combat squad where it will probably not fit in with the role of the squad. Or
MM can be good as you are chucking them in close in the rhino.
But the
ML fits bolter fire and yet fits melta fire and also gives some ranged attack
That covers a few of my thoughts