See videos on 12 pencils on YT, the only set that you shouldn't buy the 12 of that I've found is the Cretacolor Karmina's, difficult to get rich mixes and you cannot mix a good green from the blue/yellow.
Get Alyona Nickleson's book.
Some people use solvents to blend the wax of the colors together or scratch off part of the surface with a blade to relayer.
This book also helps a lot
Colored Pencil Painting Bible: Techniques for Achieving Luminous Color and Ultrarealistic Effects https://smile.amazon.com/dp/0823099202/ref=cm_sw_r_cp_api_i_YYBoFbYGHCBK8
Actually, I think if they wanted to try some special techniques, the difference may prove to be important in certain instances. I was thinking of the coloring pencil technique I read in my book, Color Pencil Painting Bible, using a solvent like gamsol to help blend strokes and deepen colors. I believe that only works with traditional wax/oil-based color pencils. But it's been a while since I read the book or used the technique myself, so I could be mixing up the details @_@ .
I think its just a manufacturing thing, when comparing like for like they become more obvious? Another advantage of Polys are because they are oil based you wont get wax bloom.
http://thevirtualinstructor.com/blog/prevent-colored-pencil-wax-bloom
Yeah there are so many techniques for blending with fluids, burnishers and blending pencils etc, cross hatching etc etc. They are so similar in many ways that you treat them the same, as i say, i use polys and luminance together, one is oil, the other wax and they blend together and layer without issue. I've got the full set of 120 polys and working my way through the Luminance, 20 to go, just purely as its easier to grab a colour "ready made" as opposed to blending yourself(though you still have to blend to get extra colours" and i may even add 20-30 of the Caran D Pablo's to that too, if needed.
Also there a book called colored pencil painting bible, highly recommended by so many.
https://www.amazon.co.uk/Colored-Pencil-Painting-Bible-Ultra-realistic/dp/0823099202
Edit: Forgot to add, whichever pencils you go for, but a Luminance white pencil, its the best white out there by far.
The Colored Pencil Painting Bible is a great resource for learning colored pencil technique.