Deaf, my favorite manual safety add-on for those who want one on a Glock is the one developed by Joe Comminolli (hope I spelled that right). It's a thumb safety mounted on the frame, very ergonomic, works like a 1911's in that up is "safe" and down is "fire." Can be quickly and economically installed by Rick Devoid at Tarnhelm, www.tarnhelm.com
. Only down side is that it's right hand only.