Paddling Magazine ran a good FAQ on the new Level 50 PFD's that are now classified by the US Coast Guard and Transport Canada. It is essentially a low profile, low floatation PFD, with only 50 nm of bouyancy (about 11 pounds, less than the typical 15 or more pounds of Type 3 or above vests). The goal is to make PFD's less obtrusive so hopefully paddle boarders and anglers will actually wear them!
This is a good experiment - I'm looking forward to what the data says once these are available. Read the article here. You can also find out more about the Level 50's for different water sports at the Water Sports Foundation, here.
While we are at it, why does every boat, paddle power or otherwise, not come with a new PFD?