Impressions from the first use of the Visco Parts head KEF-52:
Excellent head for cutting with immediate ease of changing the line (3.9mm). Unscrews by hand. Line change approximately every 1-15 hours of use.
It was used on 2 3hp machines. Line changed for trimming after every 1 tank of fuel for rest. Since the temperatures were high at 39° and I had many hours of cutting (15h). Grass, weeds of 1 meter were cut in an area of 6 acres. Experience with many heads. A worthwhile purchase. I recommend it to you! Unfortunately, I did not buy it from skroutz and I paid 15€ instead of the 8€ that the platform has it for. I will buy another one.

I put it yesterday in a local workshop, replacing the worn-out two-way Oregon that I had been using for many years. Supposedly, the screw loosens by hand to pass the fishing line. I immediately got frustrated with the first change of fishing line. It tightens so much that it doesn't unscrew at all. I wasted my day hitting the plastic disc with a hammer and chisel to loosen it and change the fishing line. In 5 hours, I barely managed to cut the grass in an acre of olive trees... If it hits a hard branch, then the fishing line gets cut and becomes useless. The most unusable thing I have ever used. Unacceptable! 15€ wasted, (a rip-off in our village...)
I went back to the workshop and exchanged it for an Oregon type worth 25€. (Testing and review coming soon.)
Discussing it with a friend of mine, he told me that he faced exactly the same problem with it and threw it away in less than an hour of use, after the third attempt to change the fishing line! I tortured myself even more...