Nope, you don't NEED a Rotor. There are many loaders out there that will load paint at a reasonable speed and for less money; and if you're capped on your BPS, what more do you need?
That being said, I have one. They're very strong, very reliable, a piece of piddle to take apart and the batteries seem to last forever.
As said above, it comes down to your budget, the shape and weight your after and all those kinds of things. Aesthetically they very nice and have a low profile.
Like I said, do you need one? No. Do I recommend one? Yes.