Buoyancy aids are used most commonly by kayakers, canoeists, paddle boarders and dinghy sailors.
They are designed as a flotation aid, rather than a life-saving device and have several key differences to lifejackets. Regardless of the specification of buoyancy aids, they do not provide (nor are they intended to) the same high level of protection as lifejackets.
Force 4 Guides:
Video: Buoyancy Aids vs Impact Vests