A few questions about Shelix cutterheads

I was looking at those aftermarket shelix jointer cutterheads, and
there are a few things that are bugging me.

First, how do you get a flat cut with them (as opposed to a plain
helix, where the cutters aren't twisted to "slice" the wood)? Any time
you take a straight blade on a cylinder and twist it away from the
axis of the cylinder, the *ends* of the blade are going to stick out
further than the center. To help visualize this, imagine if your 6"
jointer knifes were turned in a helical way (for example, with the
right edge hitting the workpiece first, and the left edge last) so
that they "sliced" through the wood. Now, imagine that they were
*really* turned... like 45 degrees. In your mind's eye, do you see how
the ends of the blade would cut deeper than the middle? It seems like
that would happen on even short blades like those on the shelix, so
that you'd get a slight wave (or anti-cove) effect on the workpiece.
Of course, they could fix this by making very carefully curved cutter
inserts, but I've never seen any ads for "shelix" inserts versus the
"helix" ones, so I'm not sure that they're doing this. Can anyone shed
some light on this?

Second, how do you make the cutterhead parallel with the table along
its width? With my existing knife-type cutterhead, I'm able to use
jack screws or a magnetic knife setter to adjust this. It appears
that, with a shelix (or a plain helix, for that matter), if the
bearing seats aren't perfectly parallel with the width of your table,
you've got problems. How do you solve this? Do you put shims under the
bearings? Do you tweak the table? What?

Lastly, are the individual cutter-squares usually carbide or just HSS?

- Joe