We just called them Turtles
We used turtles for years on my boats. They were a bag that had a large metal ring around the top of the bag and the cover which was attached by a cord and had a rubber ring inside which could snap around the ring. The crew would attached the bag with spinnaker in the front of the boat with the three ends of the sail peeking out of the bag. When it was time to go for the spinnaker, we would attach the halyard and get the pole ready (no pole for the asymetrical). Both sheets would have already been attached before we started the race.When it was time to haul the spinnaker, we would just haul on the halyard and the top of the turtle would just pop off releasing the spinnaker.In some ways I do find it easier than the sock. However, you had to pack the spinnaker carefully in the turtle for everything to work. We used a spinnaker gun (West Marine) and rubber bands and generally did better than the competition.Hope this helps.