* The Tybloc will reduce the line strength to about 2000 pounds, based on the testing I've seen. Probably OK for a short tether, but too low for a tight jackline.
Sail Delmarva: Sample Calculations for Jackline Stress and Energy Absorption
* Seems too fiddly to use in rough conditions. I would favor short tethers (3 feet) and conventional jacklines, even on a 27-foot boat. The adjustable tethers I might like. I use dual length (3'/6') tethers and they suit my boat fine, but I would go shorter on a smaller boat, perhaps 2'/4'.
* Look at the Kong Tango. Tango Carabiner : Rock Climbing Gear : Rockclimbing.com
. I've been using these for a while. Fast.
I've used Tyblocs climbing (hauling and to prevent slack from sliding back when simulclimbing), but they really aren't meant to take fall impact. No accender is.