The Gadget from Tau Development Group has been out of its testing phase and available to consumers for awhile now, but its something that isn’t extremely widely known or popular. If you carry a Glock regularly, this piece of hardware will give you additional peace of mind when re-holstering at a cost of $79.
For people who carry a Glock, particularly inside-the-waistband, and even more so for those who carry at the appendix position, this device allows you to keep your thumb on the backplate of the slide and apply pressure to the striker–the same method used by carriers of hammer-fired guns. This mitigates the possibility of a negligent discharge while holstering in the case of your shirt getting caught in the trigger guard.
It may not be for everybody, but i find the added control when re-holstering while training from the appendix-carry position to be worth the cost.