I stick one of these in my backpocket every single day. I've filled up eight of them in a year. They have a nice flexible spine that's durable and molds to your body–I rarely am aware that it's even in my pocket sitting down, but whenever I need something to write on, I always have a beautifully personalized artifact on hand to record my thoughts as a combination diary/to do list/everything else etchpad. I ramble. But these are seriously the best.
I would buy them if they were five times as expensive, knowing their quality and versatile application like I do now.