Well then, here's some more from the internet.
The bolt does hit the back of the receiver. You can test this for yourself if you take one apart and compare the bolt travel with and without the spring. It will be the same. By the way, springs are never designed to run to full compression, as they would be over stressed and need replacement much sooner.
The back of the bolt has been designed to bear against that area of the receiver. That was the plan. Now when it hits, there will be an impact or impulse and that is what this sort of buffer absorbs. The reduced impact force will increase the longevity of any optics you have on the gun, especially NC star optics. Unless you are super sensitive, your shoulder will not be able to tell how fast the bolt stopped when it hit the backstop (unless you hear the clank, I suppose, I've never heard that either).
Besides optics, if one had an sks that had been shot for lets say 10,000 rounds, there may be some "flattening" that has occurred at the back of the receiver in the impact area. Since this area is very beefy, it is not an issue of the sks wearing out.
I designed one a few years ago for the purpose of protecting scopes and sold a few on this forum. Just never go around to making any more. If you do a bit of searching on my Username you can find some further comments there.
In answer to the OP, the Russian one shown will work, however, they will need to be replaced and they need to be made out of a certain material that can handle the compressive loads. Yes, they are substantial. That is why I choose a different path to address the issue. I use them in my Sks and they do work. At least in my opinion.
Hope this helps.
I've heard bad things can happen with those buffers(all on the internet of course, so take that as you will). The bolt is designed to not impact the rear of the receiver, the spring takes the force. If you add material in you can have the bolt bottoming out on the back of the receiver where it's not supposed to be impacting or short stroking like Beer said.