lawn aerator for throw and mow?

My brother-in-law used one on his fourth-year T&M plot this year. Last year it didn't do well because it had very little vegetation to mow over the seed. He had poor germination that year and the birds really did a number on his seed. This year he worked it over pretty well with a barrel style lawn aerator before throwing seed, and then one pass after throwing seed. The results were excellent.
How much thatch was on there when he did this? And do you know if it was a spike or plug-type aerator?