I think you are probably talking about recoil springs/guide rods. The heavier ones will help balance the pistol to give it a better feel in recoil. The reduced power recoil springs let the slide travel faster and set up a new cadence to the recoil cycle that may reduce felt recoil and bring the gun back onto target quicker.

A weighted guide rod in a small pistol will have no felt effect in muzzle flip. In addition the accuracy will not improve. Cheapest and best way to improve this is to work on proper grip. I used to be amazed watching some people shoot fast with no noticeable muzzle flip and I couldn't. I then started practicing with a good thumbs forward grip and can now shoot fast pretty accurately. This was all due having the proper grip.

There is no way for the guide rod to help tighten groups with proper ammo. The weighted rods can help reduce recoil very slightly, just due to the weight. You could get more reduction by putting a light on the trail instead... Much more sight. Save your money and buy ammo :-)