Choosing a faction can be a hard thing to do in Dying Light 2. There are many upgrades on both factions’ upgrade list that are indeed worth it. The PK Razor Cannon is one of those with only taking level 2 to get.
You can certainly unlock the razor cannon in the sector you deem appropriate while still mostly giving power to the survivors. Ultimately the choice is yours. Hope we can help you choose.
Above is video of the PK Razor Cannon being used on the spot.
It makes quick work of regular infected and even some more powerful variants. Hope you like it, enjoy!