Force 6 products are specialty products designed for swifwater rescue. Here is the web page for their PFDs:
Force 6 PFDs

While self-rescue (paddling if engine goes down) in an inflatable boat is a potential event that must be taken into consideration, it is not primary function and therefore the PFDs are not designed with paddling comfort in mind.

The PFD allows for both defensive and offensive swimming, but like most PFDs, it does limit you slightly.

The tether/leash or blow-out strap is for live bait rescues where the rescuer is attached to a line, enters the water and makes contact with the victim. The blow-out feature allows the rescue to disengage the line if the force of the water is over powering the floatation. Think of a person at the end of a completed played out line. As the water flows over the person, the water pressure will tend to force the person down under the water, the blow-out feature allows the rescuer to separate from the line, thus allowing them to freely float down stream to either self-rescue or to be rescued from boat or shore.

If you look at this video around 1:13 and 2:52, 4:53, you will see how a tethered swimmer is being forced down under water. The blow-out strap/tether allows him/her to free themselves from the line and travel downstream.

Swiftwater Rescue Techniques

For suspension, a separate harness worn under the PFD would be necessary.
For example: CMC SRT Harness

Pete