For what it's worth... I mainly used AltTab to switch between apps, but for certain purposes also the KM App Switcher. Both with the shortcut ⌘+tab. When "Space" is down, the KM app switcher opens, otherwise AltTab.
I think with or without "Space" you can use every shortcut twice, without conflict. This has only recently become clear to me. I find this useful. I'm posting a general example in case someone did not know that either and wants to try.
Action 1 - ⌘+letter (Space UP)
Action 2 - ⌘+letter (Space DOWN)