2 years ago, I bought a DOL-Fin X-20 from SmithAerospace looking for a comfortable monofin (but also mainly out of curiosity for that new concept). I made several posts about it in the past but now, 2 years later, I would like to make a short final report about it.
Concerning comfort, no doubt about it because I participated to the "CAP24Apnea challenge" last year meaning 4 times 2hours of 50m DYN series in one row (with 4hours rest in between^^) totalling more than 10km and my feet were just fine. It was not really the case for the other freedivers wearing Glide-fin for instance :-).
Concerning efficiency, have a look at the two video's hereunder that compare the X-20 to an hyperfin (stiffness nr. 2, angle of ca. 28deg from Starfins). These video were made at about the same time, meaning that I had very little training with the fins before the video shooting.
October 30th, 2012
December 18th, 2014 (Video by Cédric Bourgaux).
About 4 times "kick-kick-kick-glide" for the X-20 and...about 3 times "kick-kick-glide" with the hyperfin for 25m.
Besides the numbers, and as a general feeling, the X-20 thrust is working well but the ratio "force supplied to the fin to thrust obtained" is much smaller with the hyperfin and the "glide feeling" is much higher according to me. Dominique Jacquemin, a 20 years experienced freediver (including about 10 years with a glide-fin) had the same feeling and actually sold his X-20 after 6 months, to go back to his Glide-Fin.
Last but not least, the X-20 has the big disadvantage not to have any buoyancy. As a consequence I was not able to maintain an hydrodynamic position during free falling in constant weight. Ron Smith is actually proposing to add buoyancy to the X-20 by adding himself pieces of wood (but with 200 extra USD-exclusive shipping cost back and forward-, I found it too much for a trial). This year, the DOL-Fin Orca Mk-2 came out. This is probably the response to the issues mentioned above but because it is three times the price of an hyperfin, my sense of curiosity was quite diminished :D.
Indeed, I'm really enjoying my Starfins, a true piece of art, beautiful, soft...Great job from Alex Lichenko! I could not believe Eric Van Riet Paap when he told me that he was almost in love with his Starfins...I start to believe now :D.
Well, this is it. A simple report from a simple non-competitive freediver but hopefully this helps. In any case, don't hesitate to contact me if you have any question;-).