Now that I've had my custom molded earpiece for a while, I'll chime in here. What good is that it's quite comfortable in the ear. Once you get it snapped in, it's quite light and pleasant. It's not pushing your ear canal to be wider, like normal earplugs or canal-phones do.

Sound quality, sadly, is no improvement over the stock rubber bits that came with my Jawbone. High frequencies are still seriously attenuated.