This is a great tool to be used in addition to or independent from a pull buoy for training.  However, it will be too big for juniors or kids (had to wrap it around one foot twice for a smaller swimmer the other day).  Durable and sturdy.

Easy on/off. Not quite as comfortable as cushioned ankle lock, but does good job of keeping feet together.  Generally use with pull buoy.

I have been looking for something which can be used above the knees to keep them together when swimming breast stroke and butterfly. When I saw this and the price is very reasonable, so I ordered one and tried it on my son (10 years old) by putting it just above the knees it when doing the dry-land with stretchcordz for the frog kick. It works quite well in dry-land and I am sure that it will work well in the water. You can also use it when doing squarts, side steps in dry-land too and anything you can think of. More importantly, it is only $5.39 and more than just an ankle band for pulling!