Hi
I have not taken the Mares X-streams on a dive yet, but I have been out snorkeling a number of times with them this week. They are very light, that's the first thing that struck me. I was snorkeling in very shallow water at times in very narrow channels and I found these fins to be easy to maneuver with and also great to hover with.
They responded well to little flutter kicks and when I took them out into deep water they seemed to be powerful with a bigger kick.
They seem fairly powerful but they do not accelerate or have the "bite" that my old jet fins have. I could swim fast with the x-streams, but maybe not quite as fast as with the jets. I was in the water for an hour to and hour and a half at a time, sometimes going a fair distance, and did not experience any fatigue from these fins. They do seem to be very easy on the feet and knees.
I like them a lot and I want to get into some heavier current and compare them to the jets. Also they seem to have more positive flotation that the jets. I'll try dropping them in the water tomorrow and see what happens.
I plant to rent a pair of Scuba Pro Twin Jet Max fins this week if I can find them and compare further, but so far I really like the X-Stream fins.