I'm running a free-float KAC RAS on my rifle. The main advantages of the free-float is that the barrel is now independent of the handguards, so adding accessories to the rails, torquing hard on the sling and other changes don't affect your zero.
On my own personal shooting, a free-float let me tighten up my groups by about 0.5" at 100yds but only from a stable, solid position. In kneeling or standing, I don't think the position is solid enough you'll be able to appreciate the difference.
From a military use perspective, the free-float also distributes weight of accessories better. In a standard military RAS, all of the weight of the rails and handguards is attached to the barrel. Add heat and an aluminium receiver to a lot of accessory weight hanging off the barrel like a lever and the barrel extension can be moved out of alignment enough that the bolt of the weapon will batter itself on the extension. On a free-float, the load is usually better distributed (though different systems do it different ways).
Which free-float tube are you looking at? Most of them require higher-level maintenance to install if you are modifying a service weapon.