It would cost a fortune to have a variety of paddles to fit every size of paddler. So at the family cottage, in rentals shops or SUP schools you'll probably want an adjustable. After all, with an adjustable paddle, one size fits (almost) all. One piece fixed length paddles have no moving parts so they transfer power more efficiently. That's why racers and 'serious' distance paddlers always use a one-piece paddle. No moving parts can also mean that your 'fixed length' SUP-paddle will last longer than an adjustable.