I have the packers and they are easier to get into, and especially to close, than my roller dry bags for Kayaking. It's true that the straps can flap around but there are ways to tuck them in or tie them off. I am pleased with the Packer Plus'.
I would think that the Rollers would survive total emersion in a stream, though, so if you absolutely positively need the waterproofness of a dry bag then that would be a driving factor in favor of the Rollers.