Considerations - How to decide which Inflatable Lifejacket (PFD) is for you
There is one more feature separate from the inflation to consider. Type V PFDs can also have harnesses, especially beneficial for sailors. For those unfamiliar with this, you wear a harness and use a leash to clip into a protection point (often in the cockpit) or to go forward to, clipped onto a jackline to do work up forward.
Automatic PFD vs. Manual PFD
Automatic is supposed to inflate on contact with water - and it takes green water, not just spray, to make it inflate. An automatic inflation type V could save your life if you were knocked unconscious while going overboard. An automatic inflatables could also inflate inconveniently if you are sailing in a HobyCat, plunge through a wave while on the bow or any other time you get water dumped on you.
The manual inflatable requires you to be conscious and aware of what you are doing to pull the release for the cylinder. This is the most reliable of the two inflatables and requires less servicing.
Harness or Not
You may want an inflatable PFD with a harness if you are working on deck, sailing offshore or just simply wish to stay attached to your vessel because you are single-handed or are in rough weather.
Most power boaters and inshore sailors choose an automatic inflatable PFD. Most offshore sailors choose a manually inflatable PFD. Many sailors, solo mariners and a small number of power boaters will choose an inflatable PFD with a harness. There are inflatable PFDs with removable harnesses.
Not Recommended for Some Activities
Because of the unique nature of Inflatable PFD's, they are not universally recommended for all water sports activities.
Inflatable PFDs are not recommended for non-swimmers; not for use for active watersports activities - skiing, tubing, wakeboarding, white water, or PWC
Finally, they require regular user checks and maintenance and are available in adult sizes only.