At first I didn't know what to make of this shoe/sandal... it's lightweight, comfortable and "convertible", which is a nice feature that I've never seen in a sandal before. First, I'll break down the benefits, then give the low-points.
"LIGHTWEIGHT & COMFORTABLE"
This is probably the most attractive feature of the CROC, because it adds to the comfort and makes you feel like you're walking on air. By far the most comfortable things I've ever worn and I'm a picky shoe person. I have only owned 1 pair of sandals for the past 6 years and have hated every other sandal I've tried on, so these CROCS are definitely special.
You can turn the "sandal" into a "shoe" simply by pushing forward the strap. In "shoe" mode, it's a tighter more snug fit, so you don't have to worry about it coming off your feet. In "sandal" mode, it's easy to slip on and off (although it has a tendency to cling to the bottom of your feet), for that quick trip outside to take out the trash, or pick up your cell phone that you left in the car.
PROBLEM: "SWEATY FEET"
One problem I have with the CROC is that it doesn't ventilate very well. Sure, it's got holes. But the material is such that it traps heat so you're feet end up sweating in warm weather.
PROBLEM: "HOLES ALLOW DEBRIS IN"
Another problem is that the holes allow all sorts of debris into the sandal while you're walking, such as loose rocks, wood chips at the playground, sand and dirt (when you're not at the beach), and rain water (puddles in the parking lot). This means that you're feet get dirty rather quickly and can be uncomfortable at places where there is a lot of debris - eg, playgrounds.
"SIZE & PRICE"
Sizing is a bit weird. I'd recommend going to a store first to try it on and see what size you are. It's hard to find a good selection at a store, so it's best just to dip in for sizing and then purchase the one you want on Amazon. Turned out to be the best thing for me, as I was able to score Army Green Caymans from Amazon, while searching at numerous stores I've only been able to find blue and black Caymans in sizes way too big. For $29.99 I think it's a bit pricey actually, but if you're picky about sandals like me, there's nothing you can do about it.
One other thing you'll have to get used to is how aesthetically disgusting it is. Let's be frank: it's a damn ugly shoe and there's no way getting around it. It's not the prettiest thing to wear, but it's hands-down the most comfortable. Just be careful where you tread. Definitely not an all-terrain/purpose sandal. Good for beach and casual sidewalk/short trip walking.
"DIFFERENCE BETWEEN THE BEACH AND CAYMAN STYLES"
None. Except that the sizes for Beach version are "ranges" and are more roomy for your feet. Cayman sizes are exact and are more narrow. Try on before you buy as the versions are not the same.