Results are limited to 20 (with RecentManager you can get a huge number of results)

Results are sorted by timestamp (they're not sorted by RecentManager)

Sorting and clamping of the results is done in C and only the 20 most recent results are stored in memory

The "changed" signal sent by DocSystem is delayed via idle_timeout, so your applet doesn't rebuild immediately when Gtk.RecentManager sends its signal (which could potentially reduce the speed at which apps are launched)

DocInfo provides decoded URIs and the ability to quickly create the icon so your applet doesn't need to do that itself.