Hi
I must say that i bought the Clip Studio Paint version, just because i don´t like the Manga word in the program name lol..
To answer your question.. yes is a good investment and one of the most affordables in price vs performance, if not the best.
There is nothing in Manga Studio that can´t be done in Photoshop (sketch, draw, paint, color, thumbnail, comic template, diagram, balloon, speed line, screen tone, perspective) except for vector drawing, but overall any comic related topic is more quick and practical in MS.
About editions.. Only important difference is the multi-page and 3d-2d features.. wich aren´t important to myself so i don´t have the EX edition.