Nick,
I would prefer not to swing the head to an angle. I would only do that if I had a lot of parts to make, all the same. Other than that I would use something like the digital one, or angle blocks or a sine bar. or even just a simple protractor will do. It all depends on what accuracy is called for on the job. Most of the angled stuff we do in the shop doesn't require super accuracy, near enough is usually good enough. But sometimes it has to be done spot on, hence all the different devices to achieve what is required.
I am just finishing up digging out my shop, and the first thing I will do is retram the mill. It isn't far out, maybe only a couple of thou, but enough to cause me to change my machining techniques at this time. The tram got knocked out of wack when I was playing about with the horizontal milling attachment. So big machines can still be affected by cutting big chunks out of metal.
John