I hadn't heard of Puddle Jumpers until this morning.
A Puddle Jumper is a Type V Personal Floation Device (PFD). It's "designed to provide a stable face-up position in calm water for a conscious wearer...Good for calm, inland water, or where there is good chance for fast rescue... Comfortable to wear for extended periods of time."
One of the "disadvantages" of this type of PFD is that the "wearer may have to tilt head back to avoid going face-down." Because we are using this as a swim aid, and not a PFD for boating, and because my daughter can turn to a face-up position from a face-down position in the water, I don't consider this a problem.
I also looked at swim vests, but decided against them for a couple of reasons. 1)I want my daughter to practice swimming in a swimming position. 2)I want her to be comfortable, and swim vests are bulky and have crotch straps.
Because the Puddle Jumper has a floatation band across the chest, I think it actually encouraged my daughter to lean forward and swim on her stomach, unlike arm floaties which kept her in more of a treading water position. (The cost of the Puddle Jumper is only $18, while Speedo inflatable fabric armbands - arm floaties - are $12, and the Puddle Jumper doesn't need to be inflated.)
Here is a video of my little tadpole enjoying swimming with her cousins in her Puddle Jumper: