When I went hands-on with Facebook's new launcher a few days ago, I stepped away pleased with the overall experience, but felt that it lacked a lot of the features a power user (or even a regular user who does stuff) would like. Still, I found the "lock screen" functionality to be a very pleasant experience – turning my phone on to nothing more than a scrolling photo and the time is very minimal and relaxing. I even made the comment that I wish I could use it as my lockscreen and return to Nova for my actual launcher. Turns out doing just that is actually extremely easy.
Basically, you need to set your favorite launcher as the default (you can clear this in Settings > Apps if you've already set Home as your default), but don't disable Home. If you leave the option to "see Home when screen turns on" enabled but don't actually have it set as the default launcher, then you'll see Home as the lock screen, but can return to your favorite launcher with a quick tap of the home button. It's basically the perfect balance (in my opinion) for those who wish to use Home but don't want to sacrifice the functionality of a "full" launcher.
Thanks, Maff Mace!