Easy to use and comfort..True to size. You don't need socks

This review is based primarily on fit prior to using them for snorkeling. I tried the Cressi Rondinella, Agua and Palou Long Fin Adjustible. I wear women's Size 9 athletic shoes (8.5 dress shoe).
Rondinella (blue) - Favorite! Most comfortable by far. Light weight. Flexible. Size 41/42. And, I think it's big enough to wear a water sock, if I want. I only wish it were available in pink (to easily identify mine vs my husbands). I like the full foot and feel more confident that it will stay put while snorkeling.
Palou Long Fin Adjustible - Comfortable. I liked the idea of the adjustable, so I could opt in and out of water socks. The strap did feel secure enough that I don't think it would come off; although it was easy to get on and off. The foot part fit a little tight on top of the foot; which I think helped it from moving around. It was tight, but not uncomfortable. This definitely felt heavier than the Rondinella. I did like this one though.
Agua - Size 39/40. Fit fine, but it did rub on the top of my toe near the cutout. The fin part was a harder plastic, so I was nervous about how durable it would be. This was definitely my least favorite.

Arrived on time and was perfect fit. Easy to don and comfortable. Good performance in the water.

The first pair I ordered put pressure on the sides of my big toes so I ordered the next size up and wore socks when I tried them in the pool. I love the feel of them and they really propelled me, which my last snorkel fins did not. They are a little loose but with socks I think they'll be fine. I'll know after an upcoming trip to Roatan, Honduras, where I'll be snorkeling twice a day. Fingers crossed. Oh, they are lightweight so they'll be easy to pack. My big diving fins are too heavy to pack and are not really configured for kicking on the surface. That's what makes these Cressi fins so good.

GOOD ALL AROUND FIN FOR THE POOL OR SCUBA DIVING. I'M 6'0 190 LBS SHOE SIZE 10.5.... I BOUGHT THE 8.5-9.5 AND THEY FIT VERY WELL, RUBBER IS A BIT STRETCHY SO EASY TO GET ON YOUR FEET, THE FIN IS A COMPOSITE PLASTIC, LIGHTWEIGHT BUT FLEXIBLE SO THE FIN DOES BEND AND PUSH WATER BEHIND YOU TO MOVE YOU FORWARD. I COMPARED IT TO THE LUXPARD WHICH IS WAY TOO STIFF FOR ME AND I HAVE FAIRLY STRONG LEGS, AND MY OLD DEEP SEE FINS WHICH ARE VERY FLEXIBLE, GREAT FOR POOL BUT TOO FLEXIBLE FOR SCUBA DIVING. SO THESE CRESSI RONDINELLA'S ARE MY NUMBER ONE FIN. I WOULDN'T BUY ANYTHING BIGGER OR LONGER BECAUSE THEY TAKE SO MUCH MORE STRENGTH AND CAN CAUSE CRAMPS... LIKE GOING 55 MPH ON HIWAY TO GET BEST GAS MILEAGE, PUSHING THRU WATER HAS A SWEET SPOT TOO AND BIGGER FINS WON'T MAKE YOU GO ANY FASTER.
THESE CRESSI'S ARE JUST THE RIGHT SIZE FOR ME... FIN IS 8W X 12L FROM TOE TO TIP AND 22.5 INCHES LONG OVERALL INCLUDING FOOT AND VERY LIGHT WEIGHT BUT WELL MADE.