Let's put it this way. How many of you would put a similar sign on your home for a year if you were promised the EBR, .50 cal, or custom 1911 of your choice at the end (having a break in or quitting counts as a forfeit)? Not everyone, I'm sure, but there would absolutely be some takers who would win taking that deal. My town, for example, is over 250 years old with only 1 recorded break-in all that history.
This "challenge" has more to do with crime stats than anything meaningful to the RKBA and doesn't make us look particularly bright in a debate... particularly because we are not, by and large, advertising the presence of guns in our homes... so it would be disingenuous to claim a deterrent effect (especially, as mentioned in the stats above, a significant percentage of homes have guns).
What you'd really want to show is that gun-owners are victimized less by burglary/home-invasions. I'm sure guns are a factor (as something to fear or perhaps to steal), but probably low on the list in determining whether a home is a suitable target or not. Probably first on the list is how easily they'll get away with it, something mitigated by a dog, alarm system, watchful neighbors, or ever present family more than an inanimate firearm.
We have to think critically about our own arguments if we want anti-gun people to take us seriously. The man in Minneapolis isn't the bravest, by far, all he did was apply a little common sense to his own situation (that his likelihood of proving his point far outweighs his own risk), something we have to remember to do.