I've already bought two of these fins and i'm really very happy with both of them:

I'm 5'9 and around 138 pounds. My feet are 26,5 cm (10,49 inch) long. The first one i ordered was 39-40 - stiffness Medium. I can only wear the included toe-socks in them (still a very tight fit).
I use it for pool-training (warmer water) / when i don't plan to wear it too long (max ~90min).

I got another one of the Leaderfins Hyper Carbon Monofin in the next bigger size (41-42) - also Medium. I need to wear at least 2mm full socks otherwise this one is too big (toe-socks only is not enough). I probably could even wear 4 or 5mm full-socks in it. It is more comfy and i plan to use it outdoors / in cooler water when wearing it for a longer period of time.

Be also aware that if the instep of your foot (the area after/behind the toes to the leg) is already starting very early and going up steep, you will also need a bigger size, as the entry of the fin is pretty tough and the rubber not very flexible. A friend of mine with nearly 1 inch shorter feet than me cannot even get in my smaller 39-40 fin as the entry is soon too small (he can just get the toes inside). For him the bigger 41-42 with toe-socks fits just fine (which would be too big for me - i need at least full socks). So my feet are somehow in between the two Leaderfin sizes for this monofin.

It has a weight of around 7 pounds - and therefore negative buoyancy. With my 1,5mm suit the weight of the fin is still so much that i tend to sink slowly already at water-level. That is no problem in the pool, but keep this in mind if going deep(er) and re-check the amount of additional weight you really need !

I'd also recommend getting the blade protection and the bag for this fin. Not sure about the hydro-wings - i will have the possibility to try one with these soon.

To my opinion it is overall a very good, comfortable and fast monofin (with the 22 degrees of angle), it is neither stressfull to your feet (compared to cheaper monofins and their footpocket-designs) nor does it fatigue your legs that much (as compared to bi-fins in my opinion) if you get/find the right size (that is the main-point - as the footpockets are not soft).

Quality product and descent shipping time.

I use the mono both in the sea and during pool sessions. It is well crafted and with the blade angle offers a good hydrodynamics, Foot pockets straight, but the use of the half-socks is recommended, in order not to stress toes and fore-foot

For freedivers who want a good quality mono at a reasonable price this fin is a good choice. Having an inclination of 22 degress hydrodynamics is fine, both in the pool as well as in the ocean.

I got the hyper carbon monofin with soft stiffness. I'm super happy with it. Foot pockets fit true to size. I feel like the foot pockets could be a little more comfortable. The blade material is good quality. The costomer service team is outstanding. Well made fin made with durable material. If you're looking for a monofin I would highly recommend this fin.

I had a recent problem with my monofin. The Freediver Shop responded immediately and corrected the problem. I'm amazed how quickly they took care of this and shipped me my monofin.

Thank you very much.
John Eckert

I initially thought the Hyper monofin was too heavy and the foot pockets too tight. Now that I have gotten used to it I love it. I have only used in the pool for dynamic apnea training but I'm looking forward to getting it out for deeper dives.

The Fin is a very solid build and the foot pockets are comfortable. The carbon blade is a little softer than fiberglass.. so keep that in mind when choosing stiffness. Still the fin flows nicely and Id recommend this fin for free diving depths. The guys at the support team were very helpful answering ALL my question about Monofins. They really took the time to write full answers. I also like the great variety of products that they offer. They also seem to beat every other price I found on the web. I am planning on buying another fin for my wife and I sure will be buying it from this store again!

I really like this monofins, this monofin is really very good equipment