Like with all ethics it's a somewhat subjective position. For me it crosses a line, but I bet more than a few others think its brilliant. Especially for a company in the marketing space. I wouldn't do it myself though, for the following reasons;

Respect. In business it's important to have a sense of respect, for your employees or employer, for your customers, for your competitors, and for yourself. An act like this shows a lack of respect to a competitor, and so I start to wonder who else gets trampled on on your path to success. Maybe me?

Karma. What goes around comes around. Sure this seems like a good idea when you're tiny and willing to pretty much do anything to get noticed, but don't complain when someone does the same thing to you. If some competitor hands out flyers outside your building one day, to your customers, don't come crying to me about it.

Reputation. It's one thing to be the new kid on the block. It's another to be the new kid who breaks the rules on their first day, in full view of everyone and gets away with it. Stuff like that can land you with a rep you'd rather not have.

Kudos for the first two parts of the article. Well done. It shows your creativity. The third though leaves a bit of a bad taste in the mouth. Sorry mate, but that bit is just uncool.