Polytechs are good guns, with a couple of minor problem areas. Those problem areas are easily correctable.
#1. Hammers and triggers can be soft. As was stated, replace with USGI Garand or M14 parts. Essentially the same thing. Not hard to do, though a bit of a PITA sometimes getting the trigger pin back in place. I recommend replacing the trigger pin at the same time.
#2. Issues with the sight knob. Usually it is the spring in the elevation knob that is soft and won't hold tension, so the knob won't hold zero. Replace with USGI Garand(marked up to 1200 yds) or M14(marked up to 1000 meters). Do NOT use a WCE marked M14 knob if you can avoid it.
#3. Op rod spring is often a bit undersized and soft. Replace with USGI. Might as well replace the hammer spring while you are replacing the hammer and trigger.
#4. Stock is ugly and soft Chinese Chu wood(later ones have walnut). USGI stock is a drop in, though a small spacer may need to be added next to the disconnector pin.
The biggest issue Polys have are their bolts. Which are not made properly, however, they are not unsafe. Head space runs a bit long, to military standards, not commercial. Which shortens already short brass life if one is a handloader. The fix is to replace the bolt, which can be simple, or not. But, most people don't and don't have any problems.
Other than that, Polys have good forged receivers, good chrome lined barrels, good trigger guards. I have 3, and I have fixed all these issues, whether they needed it or not.