Most every competition ski and wakeboard boat come with some kind of trailer guide, and they are welded on. They ROCK! My Nautique trailer, made by DHM, was excellent in that if you could get the bow between the guides you were on the trailer straight. Okay so it took a little more boat handling skills, but still whether the wind was howling, or launching in a river with current, they make recovery much easier. My current boat trailer doesn't have guides and I keep thinking at some point I will add some to make it easier in the surge.
I would never buy a new trailer without guide poles installed, and it has nothing to do with boat handling skills, but rather weather/water conditions. My experience launching and recovering is far more than most folks, although less than some peoples, and I still consider guides valuable. How many of you kept or keep your boat on a hoist in order to use it more? Something to be said for ease of use when you pull the boat on and off every other day.
Typically they are either carpeted bunks, a metal pole with carpet in the vertical position, or as shown in the OP's link a round 1.75" metal pole with a 2" PVC/ABS roller on it. In turn you can then put a foam cover with nylon fabric over the foam to further protect the boat. They are known to float up and off if someone drives the trailer in too deep.
I should really build a set for my boat trailer, but there are so many other projects ahead of it.