I think security films protect against impacts. If somebody takes a bat or a tire iron to your window, you would be protected from that. I'm not so sure about bullets though.

And it usually is true that the less than reputable guys do fine work. All the tint shops I called were in Newark, Paterson, Elizabeth, and Lodi, NJ, which isn't like the suburbs I live in. The tone of the guys voices are also different and you could tell they were from the city. However, they do enough cars to not mess up anything and they also do get their fair share of nice vehicles.

I just shopped around for a shop that offered a lifetime warranty and used a name brand tint. I found one and they did great work for an awesome price (<$120 for all windows on an E39). One rear quarter window does have a bubble but I haven't found the time to go back.

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