There I said it. During modding I made several tests. I took a certain savegame with a certain vehicle in a certain situation (Hawk intercepting an Escort UFO) and ran the game several times, only changing the stats of the used Accuracy booster aboard the Hawk. As the game is rather randomized I had to make many tests (with different situations) to see a general trend, but after a thorough examination i realized: Those things do NOT work. It's the same for the Missile Evasion Matrix. The effect is not there or it is so small (even with 100% stats) that it is not worth using. Don't use them, they only slow down your vehicles.
Not sure if anyone is interested in this, but I simply had to post about this. xD
Also: All the Guides/Tips/Posts/Fourm Members are right about the Cloaking Field: It is ALWAYS better to use a Large Disruptor Shield instead. Always. I made a similar test like with the Accuracy boosters, this time an Annihilator in the Alien Dimension, later a biotrans, the result was absolutely clear: The cloaking effect is always LESS helpful than another shield. There is NO reason to use the cloaking field, even when using evasive/defensive settings on an unarmed Biotrans: the additional shielding is always worth MORE than the cloak effect. Your ship survives longer and more often, and that's what counts.