You could produce your own but if you don't have access to a densitometer
it isn't worth the hassle. (And I suspect if you do you wouldn't be
asking). If you have a densitometer it is a relatively trivial job, but
only worth doing if you want not one but a reasonable number, as you can
make them at one time on a sheet of film that can then be guillotined. If
I go back to teaching alt-photo I'd probably provide them for my classes
in this way. But a few hours work and $5 of film etc isn't worth it when
you can buy one for $8.
The ones I've bought and calibrated myself have been to all practical
purposes accurate with 0.15 steps. However I haven't bought the ones you
mention. I can't see any need to buy a calibrated one for normal use.
Indeed, for most of your own testing purposes you could actually use
almost anything with clear steps in densities covering the range of your
negatives although the equal steps of the real thing are a definite
advantage.
Many of the best printers never used a step wedge. Plenty of printers
always use a step wedge more or less as a decoration to their prints! Of
course on this list there are plenty who understand how to make it a
useful tool. For some things - trying to get good tri-colour prints for
example - step wedges are pretty well essential.
Personally I think it is worth studying one of the texts on densitometry
but there is stuff on step wedges in some books and articles on alt photo
-including of course i Post-Factory Photography - which will generally
guide you in the right direction. You'll probably also find stuff on the
web.
When printing on silver halide the best print is seldom made on the grade
of paper that best matches the negative range (which is one of the things
you can determine with a step wedge.) Almost all the master printers I've
known have generally worked on different grades using dodging, burning or
chemical control of one sort or another.
When making enlarged negatives you can do those kinds of manipulation when
making the negative and then produce the final print straight. Most of the
platinum prints I made were from direct camera negatives and improved by
some burning and dodging. Of course you need to do it in a way that avoids
exposing yourself to UV.
Peter Marshall
On Fixing Shadows and elsewhere:
http://www.people.virginia.edu/~ds8s
Family Pictures, German Indications, London demonstrations &
The Buildings of London etc: http://www.spelthorne.ac.uk/pm/