They are cheap for a reason, I've used them, they are hard rubber, probably the scrap rubber from tire manufacturing.
The density of noise absorbing materials is measure in durometers. Its a measure of softness and hardness.
The fact that you need pliers to pull the rubber fan screw through the fan holes should tell you something about their hardness. Softer more noise absorbing materials can be pulled through with your fingers.
Those hard rubber fan screws/ fan plugs are basically the same durometer as the CaseLabs hard rubber feet that arrive with your order, maybe slightly softer
just to give some relative idea.
It just depends on the weight overall mass of your fans, your normal working rpms, and your sensitivity to noise, whether you want to spend more on the Nexus pure silicon grommets or less on the hard rubber fan screws.
My builds are both work rigs so silence inaudibility is important, but if noise is not an issue, you can use radiator metal screws or metal fan screws that are even less expensive. No one can decide what's best for your build except you, we can only throw out options for you.
.Edited by iBruce - 2/12/17 at 11:59am