The Here4 includes a suite of additional sensors that could technically be used to transform it into a minimally featured but fully functional autopilot. To date, I have not seen an implementation of that. However, that additional hardware adds cost that is of (at present) zero benefit to most users.
You can get a Zed-F9P based GNSS module that is comparably priced and likely more performant (as evidenced by the linked topic).
UM98x based hardware performs quite well (roughly the same as the Neo-F9P, depending on installation, configuration, and exact hardware architecture), typically at a slightly lower cost.
In any case, what you saw out of the M8P based module is typical of its performance, and any of the options I’ve mentioned so far would make a vast improvement. Unless you have an extremely well tuned Copter and very rigorous testing methodology, it’s unlikely that you’d discern a practical difference between any of the F9P or UM98x variants. Choose one that fits your budget and form factor requirements.