This will get you the most desperate employees, not the ones you want. I've got a home loan to pay, I'm not switching jobs if you can only guarantee 2 weeks of employment. And if there are multiple offers around, I'll take the 3 month or full time position, even if I'm half way through the 2 week contract.

Also, not all jobs/codebases lend themselves to being productive in 2 weeks, I'd argue they should be, but they aren't.