With two pillow-soft straps adjustable at the shoulders, two quick-slide straps at the bottom and one across the chest, you have total control over weight distribution
The easiest way to add a dropper is to add another section to your tippet with a triple surgeons knot, leaving a tag of 8 inches or so where you can tie on the second fly
Some of the more advanced designs feature locking hooks at the ankle, which both lock your foot in place and allow you to tailor your fit throughout (loose in the forefoot to accommodate swelling and tight around the ankle for stability, for example)
I was particularly impressed by the insulated tube sleeve, which actually prevents that first sip of water from getting boiling hot while sitting in the sun
Its an excellent choice if you want dependable rod holders for bank fishing in rivers, lakes, or reservoirs