I don't understand the question correctly. Can't adjust the lens correctly? 

This has no focusing capability. That said it will allow your lens to infinity focus the same way as it did on its original mount. It won’t change that. The only issue I can imagine is the quality control issue if any from adapter to adapter, manufacturer to manufacturer. Basically if your lens goes past infinity then it won’t change anything with it mounted on this adapter or any other 

Please note: our M42 adapter ring could not be suitable for Pentax Takumar Super Takumar Carl Zeiss M42 series（aperture pin does not fully depress, small tabs sticking out), as ours depresses the aperture pin all the way down

 

The longer Flange distance lens to the shorter Flange distance camera, then could use the infinity focus.
but if the shorter Flange distance lens to longer Flange distance camera, then could not use the infinity focus, you can focus on a limited distance.
the position of the infinity mark 【∞】of the telephoto lens or super telephoto lens is shifted slightly to the positive side to enable focus adjustment even when focus shift is caused due to temperature changes.The shift range is denoted by an L-shaped line, Be sure to check the focus through the viewfinder even when you shoot at infinity. 

yes, i had no problems with infinity focus with this adapter. the only FD mount lens i use anymore with my sony is a vivitar 20mm, and i pretty much only shoot infinity focus with it.