RV toilet paper is not really necessary although RV toilet paper is designed to break down easier in the RV toilet so it won't clog the black water tank like some other toilet paper could.
You can use regular toilet paper in the RV toilet as long as you use single ply toilet paper and not the thicker toilet paper.
If using regular toilet paper in the RV toilet just be sure to not use too much of it and use chemicals in the RV black water tank to help the toilet paper break down easier and faster.
Also be sure to drain the black water tank often so that it does not become clogged.
I've used regular toilet paper in my RV and it has never been an issue.
The RV toilet paper costs more and to me is not worth the extra price.
Never bought RV toilet paper and always have used regular toilet paper that is septic safe.
I just always drain and flush out my RV black water tank before it gets too full and never had any issues doing so.