Interestingly, if MEW publishes a tool build, sometimes I hear from advertisers that they have had a 'run' on that sort of item – reading about, say, a boring head can just remind people how handy they are!
But some folks (like me) would rather make than buy for several reasons:
1 – This is a hobby, it's the doing of things that matters, not what you build.
2 – Making things is a great way to learn and to better understand who tools work and develop and engineer's eye for design.
3 – it's incredibly satisfying using tools you have made yourself.
4 – sometimes there are savings – every time I need a new holder for my QCTP it costs me 1 2" length of 1" square bar and bit of wear on my dovetail cutter.
5 – for beginner projects that expand their stock of tools may be more useful than others
6 – tool builds usually pose a number of challenges in workholding, accuracy and finish and incorporate features that are useful in other contexts.
I suppose I could turn the question around and ask – If not various tools and accessories, what sort of projects should be in a book on milling for beginners?
Neil