The big dropcatchers have a lot of registrars catching on their behalf, so their success rate is higher.
One registrar = one connection pool to the registry.
I think Dynadot have only 2 credentials. Godaddy have a dozen maybe, but not as many as Snapnames or Namejet.
As for Pool I don't know many they have today. They terminated a lot of their shell registrars recently.
Using a small dropcatcher is an option for domains that you don't think will draw a lot of competition... but will still beat handreggers.