Helpful in many areas, but you always need one more as a backup...
I've been using these toggle straps for a long time, but be careful – sometimes one wrong move and you've sent one flying 5 meters overboard ;)
Unfortunately, one of the last ones I ordered wasn't properly secured and the toggle fell off immediately.
All in all, though, it's a very useful product for quickly securing your SUP to the railing or eliminating rattling. It's also great for the boom to prevent sheets from flapping... And yes, of course, for sails too...