There are free-float and non free-float versions.
The "standard" version is just like a regular handguard except not plastic and after you attach them you actually clamp them down so they don't come off or move. Takes about 10 minutes to install with only a hex wrench and no disassembly of the rifle.
The free-float version installs like any free floating AR tube and require "gunsmithing" work. This version is also much more expensive.
As to why it costs so much: they are not plastic so its a bit of metal there. Also, it gives you a ROCK SOLID mounting point for your accessories. For example, I have a bipod mounted to a standard plastic handguard and it flexes so bad I'm afraid I'm going to snap it in two. You won't see this with a RAS.
You have a stable mounting point for sights, lights, bipods, slings, forward grips, whatever that is as solid as (or very close to) the receiver itself. Well worth the money if you have a use for it. Then again, my wife has a different idea of what's "worth it" these days...