The included rms is basically red5 or a spin off of it. If you have dedicated or vps you can install it yourself with some basic linux command line codes.
Most that get vps are not familiar with linux or linux commands or understand how to install such 3rd party scripts. So if you do have vps you can hire someone to do it for you. You can purchase monthly from a 3rd party such as cyberxing.com
Or if you have the free ray installed use boonex.com free rms as far as I understand. Seems like this one has changed recently.
I haven't played with the 6.1 version too much yet, but it used to be that the main differnce was the video part. With rms your members could video one another in chat or im and not with no rms. They could still text chat and text im but no video. Profile videos did require an rms server whether your own or 3rd party.
So it seemed it was mostly related to video.
Now in 6.1 I keep reading about if you have adfree you need your own or 3rd party rms. This wasn't the case in pre-6.1. Either worked, so I can not totally say for sure without further testing at the moment.
Maybe someone else could verify that?
gameutopia