I have a hinge from the unknownbbq on my WSM 22.5. When I ordered it, I was leery of spending $40 + $7 shipping on a hinge. I have to say, it's a steal at twice the price! I can't speak to the kettle hinge but I really can't recommend it enough for the WSM.
Installation was quite easy, it comes with instructions. Drilled six holes, put a little high temp paint on the exposed metal with a small brush and then bolted it on with the provided hardware. When you open it fully, there is a notch it slips into to keep it open. It requires two hands to close it, one hand on each handle, lift slightly to get it out of the notch and close, very simple operation. It has a pull pin so you can easily remove the lid from the smoker if the need arises.
I think my cover would fit with the hinge attached if I didn't also have handles added to the center section. As for the lid acting as a sail, I haven't had an issue with it. I could see it being a problem if you are cooking in extremely gusty weather. If that is the case you might want to pull the pin and not use the hinge on a day like that.
If you have a WSM, purchase one of these hinges, you will not regret it.