I just got back from a Grand Canyon trip a week ago and picked up a pair of Muck Boots on my way down. All I gotta say is they were a total life saver and I was kicking myself for not getting a pair and using them on the river sooner. I wore them every day and usually most of the day. Its so nice being to just hop out of the boat and not worry about getting your feet wet. Just gotta make sure water doesn't go over the top of the boot. Even then, at least with the pair I got, only a tiny bit of water would get in since they are pretty tight around the top. I'd use a cam strap sometimes to make sure. I never had them leak through the Neoprene uppers. I'd even wear them during the day while going downriver since I was rowing my Dory and it always has a bit of water in the captains footwell. They even make pretty good hiking boots as long as you don't need to climb up stuff with tiny toe holds.
The only real downside is they trap whatever moisture does get into the boot all day, whether its just sweat or if you get a bit of water in. I wore a pair of wool socks in them, and it definitely felt a bit swampy and gross at the end of the day. My feet haven't stunk that bad since middle school gym class. I felt the need to wash those socks more then I would have thought and my feet too. Super Salve was surprisingly helpful but was still just a bandaid. Still totally worth it.
I think that was by far my best pre-trip purchase and I was so glad to have them. I never really felt all that cold and I give most of the credit to those boots. Combined with some synthetic down booties...my feet were basically toasty warm the whole trip.
The ones I ended up getting were the Cabelas 5mm Muck Boots. Plenty of other options there, but the rest felt like overkill. The $79 price tag was just what I was looking for too.
Cabela's Outdoor Rubber Boots for Men | Cabela's
I wore them through Lava over my Drysuit... Celebrating at Tequila Beach with toasty warm toes(the Tequila helped...but I was still super comfortable)...
I definitely got water in my boots that day...but it was nearly as much as you would think after running the "biggest rapid in the canyon" (that we didn't scout and all did awesome) and then trudged around in the water, hiked up to watch another group go through up the bank...and so on. Maybe had half a cup of water in each boot...probably less.
So....highly recommend getting a pair especially for cold weather or water trips. Just make sure you bring something to combat the stink since it is FOR REAL.