A couple things - first, he links to the Cato WP (as Don did earlier), but I want to make sure everyone knows this is forthcoming in the Journal of Macroeconomics. I'm not sure if any major adjustments have been made between the WP and the article.
Second, LK highlights the interesting point that in an attempt to provide an argument against the Fed, they actually note the importance of fiscal stabilization policy.
Third - again - forget all the details that LK highlights (sorry LK!) - it's simply not a valid evaluation method. Their impact estimate is not identified.