I like the Wacom a lot.
One decision you have to make is whether it’s in addition to your mouse and you only use it draw shapes, or if it is a replacement for your mouse? A lot of people use the combo and then find that it’s easier to stay on the mouse or keyboard rather than switch, also because you leave your Wacom to the side then where it’s hard to reach, because you need to keep the mouse or trackball near. So it becomes under utilized. If you do use it a s mouse replacement, then the issue becomes how you type and what do with the pen. You get used to typing with the pen between your fingers for short things like filenames, but will put it down for longer typing like emails.
I’ve tried hybrid (tablet & mouse) and never find it satisfying. So on my VFX system, I no longer have a mouse. I use the pen for everything, driving Flame, Nuke, Resolve, and OS/email, etc. Takes a bit getting used to, but you can fly through things very fast once you’re there. Absolute positioning for the win. On my editing system I have a Kensington trackball. I spend about 50/50 of my time on these systems. That prevents the repetitive motion that kills your arms.
The buttons on the tablet are useful for modifiers if you keep the tablet centered in front of you for extended painting sessions. But short of that, if it’s to the side because you keep your keyboard in the center spot, those buttons are not as ergonomic for modifiers. You can still put a few shortcuts on it. For example Undo is helpful, so you don’t need two fingers on the keyboard, you can just reach with one finger while holding the pen. Think about a few frequent two finger shortcuts and program them. There’s also a way to zoom in for precision if you need that with a small tablet.
Buttons on the pen divide people a lot. I keep the right click on the bottom and the middle click on the top, but other people switch them around. Depends a bit on the software you use, and whether you need middle click/drag. Experiment. One thing that gets tricky is double click - you can double tap but the pen has to stay in position (see below on precision). Some people put double click on one of the buttons, but then you lose access to middle click.
You should also look at the mapping if you have two monitors, as many do. You can map it just to the left monitor if you just use it for shape drawing, but probably want it mapped full if you use instead of mouse. If you have large high-res 27" monitors and two of them, the Pro S will be challenge, because the resolution of the tablet vs. the 5000px across both screens makes it impossible to be precise. For a long time I had the Pro M, but a year ago upgraded to the Pro L and like that a lot. Of course it takes up a lot of desk real estate, but if that serves as your mouse it’s ok.
You can also experiment with the touch function. I’ve found it to be good, and used it for quite some time. Especially on a Mac it will work the same way as an Apple touch pad with all the gestures, which is cool. That can help with some things when you don’t need the pen, but don’t want to use a mouse.