I used them on my last N scale layout. There are no "transitions", the one weak point of the system, but understandable from a manufacturing standpoint and easily remedied. A little bit of lightweight spackle at the bottom and some sandpaper or shur-form tool at the top will do your vertical easments nicely. The inclines should be wide enough for double-track in Z scale.
I made a couple of mistakes when building my layout:
1) not rounding the hilltop
2) putting a joint in the flex track at the top of the hill.
I had to cut out a section at the top and smooth the sharp "vertical corner".
One thing to keep in mind - it's trivial to make more short pieces out of the taller ones - simply put the riser between two yardsticks and use a hot-wire foam cutter.
Both are simple to do, and can be done the same way:
Clamp two yardsticks on the "too tall" riser, one on each side and level with each other. Use the hot-wire foam cutter along the top of the yardsticks, cutting the inclined top from the now-level bottom.
You can do the same with your own foam to make inclines, but if you want to bend them you'll need to make the "sawtooth" cuts in the sides to make them flexible, too. Easier to do that first, then cut the incline.