I wonder how does it compare to the old WellPlanner mod...
https://mods.factorio.com/mod/WellPlanner
Is it the same thing?

I'd not found the WellPlanner mod, but indeed it looks very similar to this one.

It's a little sad that at least two other mods existed with this functionality (WellPlanner and P.U.M.P.), but I couldn't find either when I searched and thus created my own.

Yeah, I basically scrolled through a good quarter of the mod portal looking for different mods I may find useful recently.
It's maybe unfortunate having to do more work, still can be a reason to make the new thing better than the old one ;)
The old mod may very well be abandoned, so yours is a welcome addition.