I was skeptical at first but gave in and bought these for my college team.  A great mix between a regular paddle and the forearm fulcrum. You can definitely see the difference when the athletes wear these and I am excited to experiment with them more.  They HAVE to have their hands in the right position to pull as the device does not let you bend your wrist.  Very much like the forearm fulcrum but easier to use and of course the paddle is nice for training as well.  The Bolster is very good at teaching the "kayak paddle" or "meathook" freestyle that is so important for 50/100 speed development.  I haven't tried them with the athletes on the power tower yet but i think that will work quite well with a lower weight.  I don't know if these should ever take the place of regular paddles but I see no reason why these wouldn't be awesome for pulling sets or general aerobic swimming.  Not sure you could sprint well with them but again for aerobic swimming it can really help save the technique, especially for the 50/100 types who can't afford to be laying out flat on that hand.

In the past, some paddles actually made my stroke worse and caused my hands to cramp. These paddles helped reverse that. They keep my strokes in line, and improved my freestyle by preventing my hands from crossing in front of me as I swam.

The only negative is the way your hand fits into the loop that keeps your fingers in place. It always falls out of the paddle. Overall, still a great product!

Generally use as supported hand paddle that keeps wrist in place.  Upon purchasing I thought it might do a better job of helping keep elbow up.

These paddles really added a strength building component to my swim workout that was missing.  They are great at improving form, as they make you quite aware of the angle at which your hand enters the water.  I haven't quite figured out the little black strap that is supposed to hold the paddle to your fingers.  It falls out.  It is possible that I am attaching it improperly, but I still feel that the paddle does what it is supposed to do and is a high quality product.