Seems handy, but all the typical git caveats apply:

• "Here's a cool feature! NEVER USE IT THIS WAY OR YOU'LL RUIN YOUR WORKING DIRECTORY!"
• Here's a cool feature, it's actually old and has no standard usage so everyone you meet will be subtly misusing it differently
• Here's why you should use my workflow instead of yours: Demonstrates a process with 2 less steps but also he skips the cleanup steps so actually its the same amount of work

Fossil also supports this out of the box: you can have as many checkouts of a repo as you want against different branches, and it tries to prevent you from accidentally nesting repositories instead of opening new checkouts.