The Turtle!

[Patrick]

These originate in Hungary where I live and swim. Locally they are known as the "Turtle". It seems their brandname is StrokeStar: http://www.strokestar.org/en/index.html

The swimmer featured in their adverts currently holds the short-course world record for 200-meter breaststroke.

[King of the mountains]

Not seen these before. From their shape, looks like they're designed to smooth the flow of water over the paddle/hand, encouraging you to maximise the surface area of the hand, which is a good thing. Have you tried them Patrick - how do they "feel"?

[Patrick]

We use them almost every session, usually in one of the early sets. Because they slow you down I feel they promote good body alignment in the water (and stroke of course). Personally I don't like to push too hard when I'm wearing them - I see it as a more technical exercise. When wearing them I feel a bigger difference between swimming well and poorly. When swimming poorly with them, I have a frustrating sensation of going nowhere fast. When swimming well with them I sometimes feel like I am really motoring and then I may push a bit.
BTW a google search shows them on sale in one or two online webshops.