Chinese boring heads receive a terrible amount of bad press and compared to some German precision tooling from a company starting with W**********, they aren't even worthy to be considered as sh*te. That being out of the way, when the price-point (new) sets you apart roughly by the factor of 100, you may expect or accept (depending on the point of view) slight variations in quality and finish.
Now that we've established that these boring heads are somewhat inferior to their European counterparts, it is quite safe to assume, that the actual boring tools with their brazed on carbide are equally challenged. And this is where this post comes in. I used to have an old boring bar with TNMG16 insert that for many reasons, the main one being that the new one required a smaller pilot hole as it has no top-support of the insert, was swapped out for a TCMT16-tool on the lathe.
Now the old tool had a 20mm shaft, milled down top and bottom to 16mm, so it was necessary to turn it down to 12mm to fit into the boring head.
Fit it into the boring head and tighten the locking screw VERY tight once so you have a mark.
Also while I was at it, all the Chinesium set screws were replaced with genuine 8.8 stuff from my local hardware store.
Then just quickly run over that mark with the 6mm endmill and make a nice flat, so that even in the unlikely case of the set-screw coming loose, I don't end up with the boring bar flying through the room.
And the final article. This should have enough length to bore XV or XT engine cases without removing the case studs, should the need arise.
And compared to the old tooling, which had a 12mm shank, but then tapered down to approx 6mm, this should be a lot beefier resulting in nicer cuts.