I have previously posted about both the engraving and the loose tenon. The tenon was fixed in a few minutes by the dealer where I bought the sax, and the engraving, while unfortunate, is irrelevant. If I want to look at nice engraving, I'll pull out my Chateau alto or sop. The engraving is the only issue I have with the finish of the Yany, and the build quality is superior to any sax I have owned, so I'm not sure what you are referring to in that regard. Is it just the tenon fit?I, too, have a TW01. As with yours, the engraving is not the best I've ever seen. Also, I had to have the neck tenon worked on as the crook was very loose. Good instrument though, but build quality and finish does not seem anywhere near as good as that of my A880 which is about thirty five years old .
Addressing the original question, I would keep the original Yany case. The fit of that case to the sax could not be better. It is literally impossible to wiggle the instrument around when it is "snapped" into place. Best-fitting case I have seen.