Sure; it would replace the current FF tube. Installation requires a few specific tools and a vice, so you have to decide if it's worth it to spend the $100 or more on tools, or pay to have someone do it for you. Obviously, if you like to do the work yourself, or if you plan to work on several ARs over time, then the tools are a better investment.
Aside from the rails, the primary advantage will be that the FF RAS will allow much better barrel/gas tube cooling.
The best BUIS is the ARMS #40, hands down, no contest, etc. You may want to replace your front sight with a fixed (my preference) or folding front sight, since the old one has to come off anyway while installing the RAS.