Check Enclosed: The Perfect Teaser?

I got a piece of mail last week with a teaser in all caps:

CHECK ENCLOSED

Of course, I opened it. Inside was a real check made out to me in the amount of $2.50.

The beginning of the letter read:

Dear Neil,

The enclosed check for $2.50 is real. You can cash it if you choose, but I’m counting on you not to.

I sent you this check to make a point …

OK, so I haven’t cashed the check. (And I won’t.) I also haven’t made a contribution to the charity. (And I won’t.) But the teaser did its job. I opened the envelope.

Is there anyone who wouldn’t open an envelope with the teaser, CHECK ENCLOSED? (Except Bill Gates and Warren Buffet.)

Is the promise of free money a nearly perfect teaser concept?

I would think this particular mailing had a high open rate. That’s always the first major hurdle in direct mail.