Drill mode is for when you already know the keys but need some help committing them to muscle memory. Unlike Practice mode, Drill mode offers no helpful hints. Another difference is that drills are timed. You have a minute to show your skills, and when the time is up, you get a summary showing how you did. You can change the default one-minute duration.

ShortcutFoo is very responsive and fast, and its interface is free of advertising, pop-ups, and other annoyances. The free version doesn't require a user account, and lets you practice several bundles from every editor--plenty of functionality for most users.

If you wish to dig deeper, a paid account costs $9 and will also open up all of the bundles. ShortcutFoo's paid version also lets you add new shortcuts and new applications, so you can use it to learn any program.