SafeSleeve products are not tested by an FCC-approved lab. They have grossly mislead consumers. They only had tested one piece of material they claim is in their products. The consumer is given no proof that any of SafeSleeve products reduce any type of radiation. Do not bother testing their products with an RF meter because accurate testing requires a special lab that costs thousands of dollars. That’s why SafeSleeve has never had their products tested.
For now, it’s probably better not to spend too much of your time worrying: you’re surrounded by cellphone signals, Wi-Fi signals, and all other kinds of radio frequency radiation day in and out — not just when you put your phone up to your face. And until the evidence suggests otherwise, all of this is still considered less of a cancer risk than eating red meat (which you shouldn't freak out about that much either).
Perhaps more importantly, what types of radiation are causing, or likely to cause, or are suspected of causing, harm to humans? Is it the “harmonics” from the transmitter? Is it the RF from the circuitry? Is it the primary frequency on which the cell phone operates? This is important to understand. If the problem is the primary frequency on which the cell phone operates then forget the case and ditch the cell phone.
That’s why randomized controlled trials (RCTs) often yield fairly clear answers about the effectiveness of treatments compared to other study designs. (Fun fact: Scottish doctor James Lind, a clinical trial pioneer, figured out that citrus fruits seemed to have an effect on scurvy using one of the earliest RCTs.) RCTs can also be used to study whether something, like cellphone radiation, can cause disease.
The only consistently recognized biological effect of radiofrequency radiation in humans is heating. The ability of microwave ovens to heat food is one example of this effect of radiofrequency radiation. Radiofrequency exposure from cell phone use does cause heating to the area of the body where a cell phone or other device is held (e.g., the ear and head). However, it is not sufficient to measurably increase body temperature. There are no other clearly established effects on the human body from radiofrequency radiation.