My group uses all of the above. I still use the "old" right turn hand signal. Sometimes I point with my right arm. I prefer to call slowing and stopping so I keep hands on the bars more often. But there are some that use the open palm on back to signal slowing.

I can see how it might be confusing to a motorist at an intersection when a group of cyclists appear and then multiple hand signals appear, even though they probably all indicate the same thing.

Can I trust most motorists to know the basic hand signals? Can-o-worms methinks.