It works well. Have used it on my 16 (without a loop of cable as srm mentioned) and have it on the 17.
It can get hairy: Here's the thing- once you get the boat back up, all the wind is on the side of the boat that has the non-extended shroud - pretty much that is ALL that is keeping the rig in place. You have to maintain course and keep that pressure going. Go as slowly as possible with the main all out, as upwind as possible, and re-connect the extended shroud to the adjuster - top hole is OK, (as srm said "it's a challenge) - you can retune later.
This can be really tricky if you are solo- and of course, the main reason you need to use the extender is that you ARE, in fact, solo
Even before I figured this maneuver out, I never experience a dismasting or damage - its just really scary when you come about and the mast FLOPS over to the side---
I've been thinking of the water bucket system instead of the extender... anyone ever try that ?