Where there is a good match between aircraft type (ILS GS aerial / eye ht) and the PAPI installation, then a significant advantage of PAPI is that it can be used to very low altitudes – well below 200ft, during the ILS to visual transition. In addition, this feature overcomes problems of ILS GS beam instability / parabolic bending at lower altitudes (below DH).
For NPAs, providing the aircraft type wheel / eye ht meets the obstacle requirements, then PAPI is the ideal guidance system providing both deviation and some indication of deviation rate.
The apparent / actual mismatch between GS and PAPI has been discussed previously in this forum; it is generally due to aircraft size characteristics.
Because PAPI is an angular system, flying low will tend to fly the aircraft back towards the normal glideslope origin; the wheel height will determine the size of the error, which for large aircraft may be unacceptable at the threshold.
For an ILS, use PAPI as the primary approach reference after deciding that the visual conditions are sufficient to land, but don’t discard the ILS completely.
Good NPA design should align the PAPI glidepath with the visual descent point, but caution as there are some exceptions. Use PAPI when you have good visual contact, but do check the approach plates for any warnings / caution about PAPI use.