They are meant to be deployed at low speeds like 100 knots or so. When I worked on test aircraft we had them on all the aircraft, and they had speed limitations around 120 knots. Get in an unrecoverable spin, pull the handle, it would pull the tail up. Some use explosive charges and some just use springs to deploy. The spring and cable systems especially were not all that reliable, I heard recently one of the test aircraft had an accidental deployment without doing anything to ask for it. They jettisoned the chute and all was well, not sure if the chute was damaged. Pilots do not pack them, sent them off to a guy who specializes in that.