I have a Bin Fin from Chen Bin and have been using it in the pool and the ocean. I got it from the old chen bin website and dealt directly with Chen, who was very friendly and helpful during the entire process.
I bought the fin because I wanted a higher performance mono as the only fins I tried prior were a Finis Competitor and a Leaderfins Freediving with wings. I heard only good things about the Bin Fin, so I took a leap of faith and bought one.
After talking with Chen, there weren't any models per se to choose from, all I said was that I was NOT a finswimmer and that this fin would be used for apnea in the pool and ocean. I provided my height and weight and my CWT PB at the time as requested, and about a month later, I got the fin. BTW, I had to pay Chen with bank transfer, which was kind of a hassle because my bank assumed that since I was dealing with a Chinese merchant, that it must be a scam of some kind. I paid $570.
The fin arrived in one piece in a handmade cardboard conglomeration of a slapped together box, kind of like make you own box out of cardboard.
My first impression after looking at the fin was that this fin was definitely handmade!!! The rubber on the Bin Fin I received looks nothing like smooth nicely contoured rubber like the ones on the website. Instead, it looks like it was made from car inner tubes! Seriously! Look my attached pics, you can see the blue stripe and the rubber ribs - like the rubber came off lawn mower tire inner tubes! HA! Another DB member I consulted prior to buying also has the same rubber construction with his (he has 2). However, it was very well put together considering...
Also, the fin is quite heavy - Chen put ALOT of rubber on this fin. According to my imprecise bathroom scale, it weighs about 8 lbs. I have held it next to a WW Glide and the Bin Fin fin is definitely shorter - the length is 68.5 cm from the end of the heel on the footpocket to tip of the blade and is 78 cm wide. I am 170 cm tall and weigh 145 lbs (66 kilos).
The blade itself seems to be fiberglass and quite thick. An interesting feature about it is that if you hold the blade up to a light source, you can see the tapered layers of the fin where it is thicker at the base of the blade and thinner towards the edge. The hand tapered blade design is supposed to be a trademark of a Bin Fin. As far as buoyancy, the fin is negatively buoyant. In the pool, as the fin is quite heavy, once you get the momentum of the finstroke going, inertia takes over and actually helps you out. There is an angle on the footpockets, I don't know how many degrees, but it's not as much as say a WW Glide. I found that additional angle was created by the SUPER tight footpockets that actually fold your feet to create an even greater angle.
Regarding sizing of the footpockets, this fin seems like it was originally designed for finswimmers. I had to send my fin back to Chen to enlarge the footpockets - which he did free of charge. So, definitely add two or three sizes to your normal shoe size when ordering one. The entire feel of the footpocket is one of unrelenting tightness, so tight that I need to put my feet in plastic bags in order to get them in the pockets - forget about wearing any kind of sock... Once inside, my feet and toes DO NOT move at all. This fit comes at a price as I can only wear the fin for about 15 min at a time - at least right now. So, I only use it for my target dive. The upper portion of the pocket is lined with neoprene and the bottom of the pockets slope upward, which is what I suspect creates the angle - in addition to the actual bending of your feet.
Performance wise, this fin is definitely better than the two previous fins I've tried. In the pool I save around 4-5 kicks per 50m. However, for me, this fin really seems to shine in constant weight. For some reason the added mass of this fin coupled with the short blade makes for a kick that is powerful and easy to turn over quickly. I feel that when I kick, I'm really going somewhere - especially when I'm negative coming up from depth (I have taken it to 70m and the ascent took 55 sec-arms down). I've included a pic that my buddy Kurt took that shows what the fin looks like in CWT when I tried it with arms up, but you get the picture.
If you have any reservations about this fin, feel free to e-mail Chen, he was great to deal with and was truly helpful.
BTW, included with the purchase of the mono was a Chen Bin monofin bag and a pair of neoprene half-socks. Also, when I sent the fin back to Chen to have the pockets enlarged, he sent me another monofin bag with the newly enlarged fin.
