I don't really regret not getting a MIS to be honest. Cargo = money. Why sacrifice cargo for missiles when you can outrun them in a MAX?
If you look at the stats of the whale- I mean merchantman, they're basically the same in terms of armament with the MAX with possibly more with the two T4 turrets on it's hull. MAX is much smaller, while the Whale can haul more. They have the same power plant and the MM has a 7 shield, which means power might be an issue with it's guns firing along with the engines. Again I'll just push in the fact that the MAX has 4xT5 engines, when compared to the MM 2xT5 + 1xT6, for a much smaller ship.
In my opinion, the MM is just not going to be able to cut it in terms of actually being a smuggler or blockade runner with it's large body and the wings (good luck getting that through an asteroid field). It's more of a deluxe armed cargo hauler then a smuggler ship in my eyes.