I really love these Arena Vortex Evolution paddles, but I should of bought the M instead of the L. You will understand why in this Arena Vortex Evolution Review.
The resistance seems good, but for my current physical condition, the added extra water resistance of the L versus the M might be much (as shown below).
The material is good, I used them on different swimming styles and they behaved very well (front crawl, breaststroke, backstroke). For the first time I used them, I had a light soreness in my upper body muscles after the 1 hour swim, but it was light & bearable. All these strokes went really well and it only took a few laps to get used to them, especially due to the fact that they are curved and comfortable.
Currently I either used them alone after a 10 minute warm-up swimming without any gear or with the Arena PowerFin Pro in order to increase the difficulty of the workout. I am currently thinking to start doing HIIT in several months and there is an area where this gear would prove a good addition to my exercises.
I can easily state that after multiple swim session with them, they feel good, the straps are OK and you can tighten or lessen them as per your need. Ah, yes, the straps were a pain in the beginning as I looked for YouTube videos in order to tie the, but the below picture makes life easier. My current configuration is the 2nd one.
I would definitely recommend that you use these paddles in case you want to do HIIT or in case you just want to increase the difficulty of the swim in order to also stress the muscle a bit more than usual.