Doesn't matter as long as you wear it while in the yak. I've got some "designed" for fishing from a yak, and I've got the smaller horseshoe shaped ones that MUST be worn to be legal in a regular boat, and these are very comfy, light and small, I have the cabelas 2500 series. The "yak" pfd's I have are comfy but can be a bit hot during the summer months, have a couple pockets for stuff and are designed for use in a yak. Try 'em on and see which one you like best, but just wear it.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.