You made the statement that an alignment bar is required to align a headstock. I have stated that is crap. Several other people here who I know to have very extensive machining experience and who's opinions I respect enormously have said it's crap. You finished up admitting in your replies that it is crap. I respectfully suggest you accept that as fact and move on.
Not everyone on this forum is rolling in money. I've been reading parts of the forum but not commenting, however when I saw this "advice" posted I was prompted to say something as I think it's completely disrespectful and quite wrong to cause somebody to spend their hard earned money on something that they're told is, and I quote, "really, absolutely, required" when it is in fact nothing more than convenient. They don't exactly give away MT5 test bars, and I would have to think very seriously before I bought one. No wait, I did, and I didn't! If anyone else has money to throw away on that type of thing then good luck to them. As Michael has said, they're handy for other things too, but again not required if money is really tight and it may mean sacrificing something else.
On that note I'm outta here. As soon as I saw a name or two I basically knew how this was going to go, but I hope, if nothing else, it's caused some people to do their own investigations as to whether a test bar is "required" to align a headstock and then consider whether on that basis they really want to spend their money on one. I bought 400 kg worth of known grade steel off ebay that I enjoy working my way through and all for less than what they're asking for a Chinese MT3 test bar. I know which I'd rather have, other's milage may well be different.