I have two kinds of gaiters, knee high, and low cut. The knee high are great in wet brush or snow, while the low cuts work to bridge the gap between pants and the light hiking boots I prefer nowadays for most situations.

Some knee highs are virtual over boots, with a rubber rand that covers all of the hiking boot except for the sole and greatly increase warmth and dryness of the overall system. These are a little more tricky to use than the more normal type that hooks onto the front laces. I often don't worry about the strap running underneath the heel, unless I am going to be in fairly deep snow.

The low cuts are superb for keeping grass seeds and twigs out of your socks. These should not be coated - that will only serve to contain condensation inside your socks. Depending on how your boot and gaiter interface, you may or may not need to worry about an accessory strap to keep the gaiter anchored.

It is much better if you can put them on without taking off your boots.

OR makes some very nice, commonly available, relatively cheap units.

You can improvise to an amazing degree with duct tape, plastic bags, and the like.