These pens have two buttons which is typical for an EMR pen.
I tested four PW550 series pens on 2024/08/30
1x PW500S
4x PW550
I'm not good at measuring IAF but each seemed to be around 3gf.
3 of 4 of the my PW550 pens have GOOD or EXCELLENT max pressure. One outlier has an OK max pressure.
HUION
PW550
HU1006
560.0gf
99.0%
HUION
PW550
HU1008
223.6gf
99.99%
HUION
PW550
HU1009
850.0gf
100.0%
HUION
PW550S
HU1007
735.5gf
99.4%
As is typical for EMR pens, these pens have a response that bows up. All 4 hit 50% at around 100gf.
So as I often recommend, you should consider a pressure curve to linearize this response so that you have more pressure control at the lower end of the physical pressure range.