I've rode with the hollow key chain for a few hours so far and it's been fine from the first pedal, no creaking or anything. There wasn't anything wrong with my Fly Tractor chain but I needed a new 10 tooth titanium driver and fancied changing to 30/10 so changed driver, sprocket and chain at the same time so could be why there wasn't any creaking.
All I would say about the key chain is follow the instructions properly, and make sure you have a decent chain tool. The (what I thought was) decent one in our work shop had a slightly burred end on it so I couldn't get the key chain link extractor sleeve over the end of it and the cheap one I got off display didn't have enough thread to fit the sleeve over and still push the link out. Odyssey have made one especially for it and it's not too expensive so worth buying.
It's a quality idea and even though I initially looked at it as a bit gimmicky due to the Allen key links, the added strength and quality is worth the price tag.