I normally install my own parts if they are 100% drop-in, but I get nervous removing metal/plastic from my EDC pistol.
If your PF-9 is new, it probably would be drop-in. Mine was.
the only plastic that might need removing, would be from the polymer grip to increase pre/over travel just a bit. If you totally screwed that up to the point that the grip was unserviceable, a new grip is only $35-$45 from KT.
Also, I sent a message to centraltexasgunworks.com yesterday before I found out about that trigger asking what they would charge for a trigger job. This morning they replied and actually recommended the Northwood trigger. I guess they're "in-the-know" about kel-tecs. He quoted 1/2 to 1 hour of work at $65/hr. Is that a reasonable rate?
Not a bad rate. If he's familiar with the PF-9, a Half Hr is probably all he'd take to do it. It took me 45 min, but I had to play with the Hammer Block a bit. $65/Hr for Service on a firearm isn't bad.
I do have one more concern, though. If I have this modification done, what will that do to my warranty?
It will not void your warranty in any way, but if I had to send my complete pistol in for service, I'd put the factory trigger back in it before shipping to them, just to make sure that the trigger didn't 'get legs' while visiting Florida. Another reason to do it yourself.
To me, Kel-Tecs are easier to work on than Glocks. [shrug]