Is it a parking brake or an emergency brake? A girl really has to know these things. You never know when that info will come in handy.
As a parking brake it is “okay” but I usually place a chock against a wheel anyway.
If you don’t have TM 9-803 it’s a good idea to get this manual right away – TM 9-803 Willys-Overland MB and Ford Model GPW Jeep Technical Manual. It will answer many of your questions.