I know another NES member that is going from a drop-in handguard (on a carbine he's building) to a free float. Combination of issues with the gas block he originally picked mad the barrel gas port not being drilled the right size (too small). We had to cut off the old gas block, since the muzzle brake (hes a PRM inmate) was already pinned and welded in place.
Benefits to free float over drop-in is nothing on the rails will effect the POI. when your handguard is linked to the barrel, you're effecting where the bullets hit depending on what's on it, and how you're holding it. While not an issue at close ranges, it is more of a deal as you get further away.
I have
one of these coming for both me and the other NES member... At $75 each, with a single top rail, plus three shorter sections you can put where you want/need them, it's better (IMO) than a full quad rail. I plan on changing over the handguard on my DPMS carbine to one of these in the future (might go with one of the shorter versions). Another one I would consider is the MidWest Industries Gen2 SS rail. Very similar in design with the one I ordered, at a higher price point. It might be lighter than the one I'll be using, but that's not all that big of a deal for me. Especially since I plan to set mine up with a bipod.
BTW, once you've converted to a free float handguard, most also change the barrel nut. It makes changing it again, in the future, much easier. Also, most of the free float handguards are designed to continue the upper's rail so it's essentially one long rail.
If your gas block is also the front sight, you'll need to also change that. Typical parts to work with a free float handguard (different than a drop in) include a low profile gas block, barrel nut for the handguard, and front sight to go on the rail.
I would also ask why you want a full quad rail. Keep in mind, the chances of you using all of it is rather remote. You'll be getting items to cover up the unused rail sections, so they don't bite into your hand. IMO, it's easier to go with a hand guard that you can put the rails where you need/want them and leave it smooth otherwise.
