I've got one on my 21ft beneteau which comes without a topping lift. Bit of a chore to install: gettting the backing plate into the mast track, tapping into the boom, shortening the rods, etc, but worth it in the end. Anything to reduce the likelihood of decapitating the crew. I found a purchase of 4:1 on the kicker fine, though I did relocate its attachment point on the boom.
I have fitted one to my Nic 35. It works well, and adds very little to the force required to haul down the kicker [4:1]. When you release kicker and sheet, the boom bobs gently up a few inches [you can choose how far] and stays there. Only surprise is for those who are in the habit of leaning on the boom while yarning with the next-door boat in the marina: the boom sags gently under the additional weight. No topping-lift to chafe the sail, slap the mast, or turn green with algae. And just think of the saving in windage and weight!
Fitting required some fiddling to create suitable slugs to go into the slots of the mast and boom: mast slug supplied was too thin, and since my boom [original cylindrical Sparlight] has a slot, I decided to make a slug for it, too, rather than drill and tap the boom itself.
Because you can't properly scandalise the main whilst preparing to leave a harbour or mooring, or to heavily de-power it for close quarter manouvers under sail.
Well, it depends on how you secure the boom. I unclip the kicker from the mast, and hitch it to a shroud anchorage or a stanchion base. This is what I have always done. The topping-lift, of course, used to create a triangle of forces; now I shift the main halyard to the end of the boom.
I agree: you can't do this unless you keep the topping-lift for the purpose, and disengage the boomstrut each time you scandalize. Obviously, that is possible, but seems a bit silly when you've spent £175 or whatever. I decided that I had scandalized about twice in twenty years, with no particular success because the top half of the sail bears on the rigging, so it was no big deal.
On a Folkboat. My fitting isn't ideal because the vang connector at the mast is several inches above the base (nned to lower the hound it connects to) and the boomstrut foot just above this makes the angle currently less than ideal, but it works fine.
Hi I fitted one to my westerly 33 and as I do a lot of singlehanded sailing I found it a very useful bit of kit.It took a bit of fine tuning to get the lug on the boom right but was worth the effort.Very useful when reefing and stowing the main at the end of a sail,I kept the topping lift and only used it to steady the boom when not sailing.Regards John