You got it mostly right!
The percentage when you hover a curve is "scale". Mostly it's useful to know if the scale is 100%, meaning the mapping from input to output is 1:1 because both ranges are the same size. We don't want you to have to do math! It can also be useful if you know you want 25% or 200% of the speed, etc. When you change the scale, Spine has to change one of the ranges. It prefers to change the "from max" value, because the "to" values are usually what's most important. However, if a property has more than one connection, changing "from max" would change the scale for both connections, so it instead changes "to max". You can also ignore scale and just set the ranges. It's not a separate setting, it's just the ratio of the range sizes.
Clamp keeps the output values (the values set on the bones) within the right side range.
Additive is the same as the old Relative, just a better name.
Local allows you to use local or world values on each side. Note that world rotation is always 0-360, as it is just "the direction the bone is pointing". You'll get a jump when it wraps around from 0 to 360 or 360 to 0. Check Local to avoid the jump.
Note you can click to add a connection straight across, which helps make it less work when you want a simple constraint. Match with 0 mix does what you expect, but as you noted the offset is now in the ranges, except for offset X/Y.
We'd love to hear how it goes! Does it do everything you need? Is there anything missing? We are considering adding a Clamp setting to the left side.
