We went to North Sails to develop a new mylar mainsail for our class (Mosquito), they came up with the Allen-key thingy, it`s a plastic end-cap of sorts with an allen-key head in the back of it which fits over the end of the batten. It`s very neat, no string & knots hanging behind your sail, can`t come undone by itself, and reduces drag.
I`d imagine you`d have to have webbing straps sewn onto your sail to retro-fit this system to an existing sail, but that would be easy.
A few turns of the key & you get tension, if you like de-tensioning your battens & retensioning each time you sail, just remember the number of turns you undo, & put them back in next time. I tend to leave them tensioned, and I don`t lose any sleep over it. I think if you have Dacron it might be good to release the tension, I have mylar & I`m lazy.
The dig at the Hobie guys was the "just kidding" part. I used to sail a Dart 18, but found that antiquated class rules that tell you to use dacron sails and then charge you as if you`re buying kevlar, made me look at a class with more open rules. Now I buy Mylar sails which are really well put together (including the batten-ends AND battens)at a lower price than I`d pay for a dacron Dart 18 sail WITHOUT battens.
Classes which have rules that have the intention of making their boats cost less very often acchieve that, but the one-manufacturer classes don`t pass the cost saving onto the buyer, so you get an average product at an above-average price. I buy into one-design, but one-manufacturer classes are pushing the cost of sailing way beyond acceptable.

There, now I`ve had my say. I`ll post a pic of the batten tensioner when I can get my mainsail & a digital camera near eachother.

Cheers
Steve