If you only plan to do single illustrations, then PRO should be sufficient.
If you ever plan to make books (eg comics or art collections) then I'd recommend EX.
50% off is pretty good; I'd suggest getting PRO and if you can always wait for another sale if you want to get EX.
I love this software, it feels much more like a drawing and art application without being too unfamiliar to others such as Sai, and has similar layouts to Photoshop. They have a demo trial to have a play with before making the choice:
Alotta people like it, its better for drawing then photoshop, and although I like sai better it has way more options. I got it on sale a while ago, hard to go wrong for 25$
I tried manga studio. Apparently Clip Studio is the successor to it. Strangely, I avoided using MS simply because the zooming in and out using mouse wheel was slow
If you ever plan to make books (eg comics or art collections) then I'd recommend EX.
50% off is pretty good; I'd suggest getting PRO and if you can always wait for another sale if you want to get EX.
https://www.clipstudio.net/en/purchase/trial