Question about Sigma Tc-2001

I use both converters (TC-1401 and TC-2001) on the fast Sigma 120-300mm f2.8 sport. They both work well, although the 2x converter reduces the sharpness considerably.
On a low-light lens like the 150-600mm f5.0-6.3, the autofocus will no longer work. Most cameras need a starting aperture of at least f8.0 for the autofocus to work. With a 1.4x converter, the 150-600mm still has a speed of f7.1-9, which means that the autofocus would no longer work at full zoom. With the 2x converter, you would only have a speed of f10-14. If you really need the insane focal length of 1200mm, you can use the converter, but be aware that you have to focus manually and the sharpness will certainly not be perfect.

I only had it for a few minutes. I very rarely shoot without auto focus. And this converter is only for manual focus. Unfortunately, this was not in the description. So I returned it without using it.
using it.