Ken,
I'm looking forward to being able to answer your question from personal experience, and will be able to do so soon but not yet.
The photo of the floating/soft shackle attached block that you're asking about is from the Nonsuch 26U I just bought. It's currently en route to me somewhere between San Francisco and Los Angeles with a delivery crew on board. The arrangement intrigued me, looks very promising to me, and performed just fine on a test sail in San Francisco Bay in 18 kts. In addition to possibly reducing friction, I'm also hoping that it'll minimize chafing on the choker control line.
I was told it was rigged this way be an outfit called Easom Rigging in Point Richmond, CA after an earlier owner replaced the original aluminum mast with a carbon fiber one. Those folks seem to primarily specialize in rigging high end racing boats. I don't care for the colors they picked for the lines, but otherwise it looked pretty smartly done to me.
That's all I can tell you at this point.
I'm expecting delivery of the new boat Sunday or Monday.
The other photo in the post, which just shows a lashing of the block on the boom, is from my current Nonsuch 26C (currently for sale, if anyone's interested in looking at Marketplace on the INA website). For the record, the boom casting on that boat is intact -- the lashing was done proactively.
I had to replace the original choker cheek block on its mast, and did that one conventionally with another cheek block. I lucked out and avoided your thread-stripping problem, but couldn't find a block that matched the trapezoidal hole pattern of the long-out-of-production original Fico cheek block. I ended up paying an arm and a leg to get a block drilled to fit that pattern.
Tentatively, I think the floating arrangement is a good way to go. Had I thought of it when fixing the 26C, I would've tried it.
Small observation as I prepare to become a two-boat owner. The monthly cost of a slip down here is 2/3rds of what I paid in annual tuition when I went to college. The annual tuition when I went to college works out to a bit less than 5% of the annual tuition at the same university today. The boat's worth roughly 40.5 years of my annual college tuition, but only about two years of today's college tuition. Don't know if that puts waiting for my boat to sell in some sort of perspective, but it sure says something about inflation and how old I am. And, at least I know it's better to be waiting for my current boat to sell than it is to be a kid trying to get a college degree.
-- Bob
Solar Wind
Nonsuch 26C #143 (plus one, starting next week)