Personally, I'd rather have an MP-5........
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.
I have a KG 99 (which is basically a short barreled and slightly smaller overall version of the TEC 9). These guns are really not good for much in terms of accurate shooting in the semi auto versions sold to civilians. The quality isn't all that bad, they're just too large, clunky and hard to aim. A Glock 17 with a 30 round mag would be much deadlier in the hands of anyone familiar with a hand gun. OTOH, they (the whole style, the UZI, the TEC's, the KG's) make a lot of sense in the full auto SMG versions (what they were designed to be); much easier to control than full auto glocks and readily adaptable to suppressors for security use and folding stocks for more accurately aimed, longer range, use.
BTW, I also have a MAC 11/9, TEC 22, and a few others of that genre. Don't really like them, just felt an irresistable compulsion to buy them when the bans were being passed.