Sorry to say, but it does not mount optics well. First, it's mounting on the gas tube, and it's not mounting to the receiver. It's guaranteed to move.
Second, you're mounting it on a plastic rail, which is not metal, therefore it's softer, pliable to an extent, and will bend under recoil.
You have two choices for the SKS to hold zero.
1. NC Star or similar receiver cover - get one with the claws that screw into the receiver. This will hold zero, but the bad news is as soon as you shoot corrosive ammo through your SKS, you have to remove it to clean it. Zero is lost.
2. Choate or similar receiver mount - you have to drill out, tap and screw this into your receiver. If you plan to keep your SKS, hunt with it, and mount a decent scope on it, this is what you want to have. (before doing this, find a Russian SKS that shoots real nice, then go to town) The only problem is once you drill out your receiver, it's "perceived" value drops a bit. This will do NOTHING to the performance to the gun, and I have owned a few SKS's that have had holes in the receiver that still sold near what I paid for them. You can put 50 holes in your receiver and it will still fire fine.
3. Scout SKS mount - this goes on your rear sight. I have their sight on my CZ 858. It's awesome, but expensive. And you can use it as a traditional rear sight if you want to un-mount your optic.