Does this not sort of constitute Pay 2 Win? I don't play much CoD, but what little I do know is that listening to other player's footsteps is very vital, to the point where there is a perk that silences them, which is usually considered one of the most powerful perks in any game it appears.
Surely selling something to "increase the directional accuracy of sounds" is bordering into this territory?
Also, this apparently only lasts for 5 years before you presumably need to buy this again, and im not hopeful that this will transfer into whatever next year's CoD game will be.