I don't know much about the TS 107mm. The 3" Photoline Reducer/Corrector can give you a 45mm illuminated field. If you want your stated focal length, and speed, the Imaging Star 130mm f5 would give you 650mm focal length, but a slightly smaller illuminated field (42mm) and it a 6 element with inbuilt flattened.
https://www.teleskop-express.de/shop...Telescope.html
Too much choice these days.
It will be interesting to see what effect the new US 25% tariff has on Chinese manufactured scopes. The US HTS code for optical telescopes was 8% up till now. Optical equipment was certainly on the new tariff list when i had a look. If Kunming, and other Chinese manufacturers, get hit with a 25% tariff what does that do to the global market? The TAK people will be delighted, as will the US makers, I am sure.