Currently when I am wet wading I use a typical felt wading boot with
thick wading socks and gravel guards. Since I like to keep things
simple I was thinking about getting something for wading that is only
one item. Has anyone tried the Cabela's zippered wading boot? Does it
keep gravel out without wearing socks underneath?

I wear the things with a pair of fleece socks, works great for me.
I've been using them for a few years, now, and I love them. Great for
backpacking because you can sort of wring them out and crunch them down
for compact storage.