These rock. They're tough as nails and keep things out of your boots like it's their job, which of course it is. I've waked through lower thigh deep snow in them, I've been up to mid-calf in water in them and they kept me dry. You can't stand in the water, I just walked through it in order to test them.
The OR Crocodile Gaiters are a staple for what a gaiter is supposed to be. You can wear them with just about any hiking boot and they will give you supreme protection from just about anything you throw at them. They do an incredible job sealing around the boot itself and the adjustable strap makes a custom fit that much easier. They are truly waterproof, and adding the GoreTex label should be proof to that. The only downside to the standard Crocs is that the under strap is not replaceable (not without stitching on a new one yourself). You have to move up to the HD Crocs to get that feature.
I've had these for 4 years now and put them through some pretty rough abuse. So far they don't show any signs of giving up. They fit well, the materials and workmanship and excellent, and they work as advertised. If you need gaiters that will take abuse and last a long while these are definitely worth the extra cash.