There are some people who believe, rightly or wrongly, that the nastier a firearm looks, the more likely it will be to make an attacker realize the error of his ways before he has to be shot. I expect that this is true, up to a certain point. Someone who confronts a home invader with a North American Arms .22LR mini revolver will likely not get the same reaction as someone who confronts the invader with a Mossberg 500. But I don't know that the ugliness of the Tec-9 would increase its deterrent value over, say, the nice sleek lines of a Luger.
A .45 1911 isn't bad looking and has more deterrent value than either