Recent research by the NFL found that the Guardian shell decreases impact forces by $1020\%,$ however,

The level of force is not the same as a concussion risk decrease. Less force does not always mean less impact on the brain for all players.

The force reduction load must be at least $30\%$ to stop a concussion.

The decreased impact is greater in the face mask area.

The needed force decrease differs by position so the range should actually be higher in order to help all players.