Do free floats work? Most precision rifles do NOT have a sling swivel attached to the barrel. The stock is cut clear to prevent any contact in most cases. That is what improves accuracy, removing the stress from the sling.
How much MOA improvement is there for the cost? Nobody has yet quantified it, they just keep saying it does. Frankly, buying precision ammo might do as much, without all the work. Adding better optics can tighten up the shooter, too. Where you get the most improvement for the dollar spent is what counts overall.
The issue M4 is a 2MOA spec gun, will a free float for $200+ installed give you as much effective accuracy as a red dot or 2X optic for the same money? In reality, not using a tight sling could do as much, right? You wouldn't be stressing the barrel, it would just be resting on the handguard. The shoulder supports one end, a hand the other, and the grip give the trigger finger some place to hang. It's the sling that bends things and creates a need for a free float, tactically or precision.
IOBC 4-83, we just took the slings off. Less fuss or muss. Plenty of us qualified expert, it's the shooter first, then the gun. Modern shooters claim that is heresy, but I gotta ask, are they selling something, or just convincing themselves the expense was worth it? I think we are confusing the urban CQB role with full battle rattle and prisoner handling with what is needed in ground combat. Having trained Infantry and MP, I know it's two different jobs.
Free floats on M4's are about the rails. The Army issues a side sling swivel that clamps to the sight base, it's obvious an accuracy improvement wasn't the point.