The flip side is that they admit some grit and a lot of water, without much insulation. You are advised not to wear them barefoot, so allow for an insulating sock in sizing for paddling in cold conditions. Essentially, these shoes are a shell for a base layer. I don't find them to dry all that fast, possibly because of absorption and retention by the mesh material.
Not a bad piece of gear but they remind me of paddling in Converse sneakers back in the day, which go for about half the price. I'm not completely sold that the upgrade of materials justifies the significant difference in cost.
Sizing/fit: I wear a 12 in just about every pair of shoes I've ever owned, and the Hiyaks are no different. They fit fine with no socks, a 1.5 mm neoprene sock, waterproof socks, or a Smartwool like hiking sock.
Warmth: The water I paddle in is hovering just below 40 degrees right now, so a pair of waterproof or neoprene socks are a standard at this point. There's a bit of cushion around the ankle and above the heel that also works as a bit of insulation. The rest of the inner shoe is lined with an almost grid-like quilted material- Astral calls it "Airmesh" - that traps bits of air in the channels which leads to some warming. If I were standing in the sub-40 degree water for extended amounts of time, I'd have less than warm feet, but after a quick dip during loading, my feet stay plenty warm propped on my foot pegs inside my boat.
Drainage/Drying: One of the features that Astral touts about the Hiyak, along with their other shoes, is that they are better than traditional booties because of their ability to dry quicker than neoprene. If you have any neoprene gear, you're probably well versed in the potential funk associated with the material. I'm not saying that the Hiyaks will be funk-free, but they do dry quickly. The outer shell is made of a hydrophobic bombproof 1000D nylon, so not absorbing water in the first place lends to drying quickly. As for the inside of the shoe, the Airmesh allows water in, but like all synthetics, allows water to drain quickly. With drain holes in the toe and heel paired with raised bumps/channels on the insole, any water that does enter (through those drain holes, the laces, or over the top) has an easy way out. When walking the water squishes out the toe (pretty fun little squirts), and when in the boat it drains out the heel holes. One thing I really like about the drain holes is that they act almost as a scupper - with a bit of nylon just inside them, they allow water out (and in) while keeping out a lot of the dirt and sand that comes with stirring up the bottom. As far as drying goes, Astral is right, the Hiyak is dry and ready for tomorrow. I paddle every day, and when I'm done I prop them up so they can drain and they're good to go for the next day. The part that remains wet the longest is under the insole, but even that is set by paddle time.
Support: The shoes are pretty minimal; super lightweight and thin - both top and bottom. With this, they're comfortable and fine for walking around, but they don't offer a ton of support. I wouldn't want to carry my boat any serious distance on a cobbley beach with them. The insoles allow some drainage with the circle patterns on them, but also provide some cushion for the rocky entries. If you've got high arches, you're gonna need a bit of extra help. The part of the Hiyak that excels in support is the heel cup - its stout and great for resting your foot on while in your boat in true paddling fashion.
Soles: The soles on these have curved diamonds as a main tread pattern, and like high end snow tires, each diamond is siped with small zig-zig slits. The traction is about as good as it gets for such a low profile sole.
Laces: Obviously, laces are the best way to get premium fit in a shoe, and the laces in the Hiyak do exactly that. I've found that really cranking down the laces puts some unneeded pressure on certain spots and becomes uncomfortable, and preferring loose shoes (I rarely tie any shoes I wear) I usually tie them pretty loose. Because I tie them loose, the laces are a bit short, so I skip the top lace hole (like anyone does in a pair of sneakers) which I wasn't a huge fan of anyway. (I like the height of the shoe, just not having the laces tight that high on my ankle!) The Velcro strap across the top is great for keeping the laces from catching on anything inside of the boat, and also helps to keep the knot tied.
Wish Hiyaks had: A spot for the Velcro to be when not stuck across the top. I'm pretty renown for less than properly tied shoes, and they've gotta be at least almost laced up to get the strap across the top. Also, when sitting on the floor drying for tomorrow, the copious amounts of hair that my pyranees/newfie mix leaves lying around tends to gather on un-stuck Velcro. Channels under the insole would add to the drainage. Just a few grooves or a little river system would help to dry under the insole. Some side tread would add to the grippiness. It would have to be a balance between gripping the ground and not gripping everything on the inside of a kayak, but I think it would be a beneficial addition.
Overall: I was a disbeliever. I had calf high rubber boots, why did I need booties or special shoes for paddling? Wrong. The Hiyaks are awesome. I moved my foot pedals up two clicks, and now have a better, tighter stance in my kayak. Not to mention that my heels no longer overlap. It's pretty awesome having specific gear - like shoes made for cold water Sea-kayaking.