In the past, I have used such tree stand umbrellas and like its been said, they are good in LIGHT rain. I never intentionally hunt in a stiff rain, but if its on the menu to get a little drizzly, I will still hold down a stand through it, as I've learned over the years them deers like that gentle drizzle and have no problems moving around in it. The umbrellas I have used, leave a lot to be desired I must say. The screw in spike that goes into the tree, just loves to bend on ya. If you screw it into hard wood, it can be a real bear to get it out after a couple days or so...... and it WILL bend on ya. Now you can leave that in the tree, but you probably shouldn't leave the actual umbrella in the tree for many reasons, but the reason that matters most to me is the fact that they are not very rugged. It is built like a typical umbrella, the ones I have used. If the rain gets too heavy, the water will start to come through the stitching holes and drip on your head and whatever else. The one I used this year, believe it was Allen, the crown of it does not dome out completely leaving recessed area on top for the water to pool, making that dip situation even worse. If a stiff wind comes your way, fold it up or take it down before it goes inside out on you. These are easier things to deal with if you are on the ground of course.
All in all, the umbrellas do help a decent deal, but are far from perfect. I believe with a little creative thinking, you can come up with a better solution on your own, maybe for cheaper even ........ and it would work better for you and be more durable. This is something I will do for myself, when I can remember or when time permits
That's my experience with umbrellas anyways .......... good luck!