I had started same search in the past. NO Real Luck on it at the end.
Here is what was expressed.
The Best US/European designs where made at least 10 years ago! If not longer. So guess what, They where the best of the best at its time. Good thing was that their quality was posted clear and they truly live to their characteristic. You paid $200 - $400. So they sold 1 every other month. But been so old it uses old technology chips! Here is where things start making no sense. For example this Best of the best are in 20K noise figure!
Now in the other hand The latest Chinese LNBs. You pay arround $30 and $50 for the so called Titanium Satellite C2W-PLL Wideband. Many claim their posted characteristic are fake. But in general this devices offer 14K noise figure. Even when the temperature stability are not always shown. Now temperature stability did not used to mean much in the old time as it was only require by very few transponders. That is not the case today. There are many transponders where dvb-s2 HD requires such a good stability as they use fec as 8/9 for example.
Well returning ti the chines lnbs. This sell by the hundred per month so in general there is no old surplus. So the are most likely used the best latest chipset!. jijiji But their quality assurance are not allways the best!!!.
So at the end it resume to Luck. When you buy Chinese there is a chance you end up purchasing the best and another big chance that is a piece of c----p.
And if you buy an American Legacy you will get a reliable old technology that you can trust will leave to the 20K figure it reads. jijijiji. Good luck.