CELSYS advertise CSP as a "stándard tool for manga artists", but it's actually much more than that. It doesn't only include very powerful tools for doing clean lines, add text bubbles, grayscale tones, panels and cell-shading coloring but also has amazing sets of brushes that enhance your possibilities simulating real-life painting (watercolor and oil, to be specific).
Plus, CSP was developed by thinking on the professional user first and foremost, so it includes the most essential editing tools that I couldn't find in SAI, which I migrated from and which I had to use Photoshop with just to get some simple things like text done, but not anymore now that I have CSP which have it all packed in one single place. Let alone other not-essential and very VERY powerful tools like the perspective tools which is just AMAZING for doing concept art and background painting.
For last, I have to tell you about the Animation features, which prevents me to open another application any time I want to do animated frames for my game sprites, which is big, BIG PLUS for me. Before it, my typical workflow was this: Draw frames sketch in Photoshop > Export > Import into SAI/CSP just so I can paint them > Export > Import again in Premiere and After Effects just so I can join them and add effects. Not anymore now that I have CSP, it's enough to draw, paint and export all the frames in CSP and maybe I'll add another animation app for special effects.
CSP is just AMAZING, this app just came out in a time I thought I needed something like it as if I just created it by imagining it. It worth the time to try it because I'm sure you will keep it in your regular workflow, no matter if your main field is not "manga", if you do Illustration then go with it :)