I have used the Johnson Hyfield type lever for my shroud extenders on my 21SE since it was new in'89. My system does not have a wire keeper at the mast base that the 16 uses....maybe because the base of the mast is kept captive on the ball on the post....I did buy a big azz righting bag ( large enough to stand in) from Colorado Bag Company/Andrew Cook that works fine on a block and tack set up. So ,I sail with two different systems.
I even like that third system that uses a long thin inflatable black bag that attaches to a line that runs through a small block added to the comtip near the top. It automatically inflates when it makes contact with the water and keeps the boat from turtlering . This system can be lower and deflated than place a new compressed Co2 container to rearm the system I found this product online @ a British boating company. A chandler business as I remember.
Having purchased my 21SE at the Indianapolis sailboat show nearly thirty years, I can only remember capsizing maybe a dozen times the first few year and once it the last 20 years. The 21 is a heavy boat that is very stable and it has a large footprint.....which seems to hold it well to the water. I sail consecutively and I don't want to end up in the drink....with a damaged boat and someone hurt.