I'm thinking:

If Primary:
Pros:
No Slowdown while Deployed
+15% movement speed on equip (92%, almost Demoman Speed)

Cons:
-50% ammo
Still needs to be spun up
-30% Damage

If Secondary:
Pros:
+15% speed on equip (But your primary stays the same when deployed)
No need for reload

Cons:
You still have only 38 shells
-70% Pellet Count (3 pellets/shot)
Can only shoot when barrel is in place

It should only be for Heavy, That's what the creator intended, that's what we're going with

There should be reload because it's pump-action (theres a pump under the barrel chambers).
Also it should have faster fire rate since it has three barrels

i mean the stats look decent