I saw you already made your decision, but anyway.. I got Nurtural bridles both in synthetic and leather version, and a Dr. Cook type bridle, and I'd always go for the Nurtural, because the cheek straps are fixed together and won't interfere with each other. If you pull on the left rein and then on the right rein and try to release the left rein (in case your right cheek strap is crossed over the left cheek strap) it will be stuck under the other strap, completely ruining your release. The Nurtural doesn't have this problem because of the Circle-X (it also doesn't slip because of the rubber on the noseband). I'd also recommend not using a synthetic material as the release is bad, the stuff just doesn't slip.
As for what people are saying about bitless bridles like this not releasing - not true. The only thing that is fixed is the noseband, the other straps are just loosely hanging around the horse's face, until you touch the reins. Once you and your horse are well accustomed to this bridle (and you have soft hands and know to ride with gentle touches instead of hard yanks), you won't need a lot of pressure at all to get the message accross, so there's barely any possibility of the bridle pulling tight and not releasing.
And about the horses not understanding the message because of the pressure at the cheeks - think about it, the cheek straps go through rings on the nose. If you have had your average physics lesson about pulleys, you'd know that with a pulley the pressure is equally divided between both straps, meaning the noseband on that side and the cheek strap get equal pressure when you pull on the rein. The only thing that's different is that your noseband is secured around the nose and won't move, so the cheek strap ends up running through the ring and putting pressure on the opposite side of the face, which makes for a pushing action against the cheek on the other side and a pulling action on the nose. Of course this effect goes away when you pull on both reins, but if you're steering with just your reins, and especially steering with both reins, you should get a few lessons. I only use my bridle to tell my horse where to put his head and use my body to direct the rest of his.